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• SQL SERVER – Guest Posts – Feodor Georgiev – The Context of Our Database Environment – Going Beyond the Internal SQL Server Waits – Wait Type – Day 21 of 28

  - by pinaldave

  This guest post is submitted by Feodor. Feodor Georgiev is a SQL Server database specialist with extensive experience of thinking both within and outside the box. He has wide experience of different systems and solutions in the fields of architecture, scalability, performance, etc. Feodor has experience with SQL Server 2000 and later versions, and is certified in SQL Server 2008. In this article Feodor explains the server-client-server process, and concentrated on the mutual waits between client and SQL Server. This is essential in grasping the concept of waits in a ‘global’ application plan. Recently I was asked to write a blog post about the wait statistics in SQL Server and since I had been thinking about writing it for quite some time now, here it is. It is a wide-spread idea that the wait statistics in SQL Server will tell you everything about your performance. Well, almost. Or should I say – barely. The reason for this is that SQL Server is always a part of a bigger system – there are always other players in the game: whether it is a client application, web service, any other kind of data import/export process and so on. In short, the SQL Server surroundings look like this: This means that SQL Server, aside from its internal waits, also depends on external waits and settings. As we can see in the picture above, SQL Server needs to have an interface in order to communicate with the surrounding clients over the network. For this communication, SQL Server uses protocol interfaces. I will not go into detail about which protocols are best, but you can read this article. Also, review the information about the TDS (Tabular data stream). As we all know, our system is only as fast as its slowest component. This means that when we look at our environment as a whole, the SQL Server might be a victim of external pressure, no matter how well we have tuned our database server performance. Let’s dive into an example: let’s say that we have a web server, hosting a web application which is using data from our SQL Server, hosted on another server. The network card of the web server for some reason is malfunctioning (think of a hardware failure, driver failure, or just improper setup) and does not send/receive data faster than 10Mbs. On the other end, our SQL Server will not be able to send/receive data at a faster rate either. This means that the application users will notify the support team and will say: “My data is coming very slow.” Now, let’s move on to a bit more exciting example: imagine that there is a similar setup as the example above – one web server and one database server, and the application is not using any stored procedure calls, but instead for every user request the application is sending 80kb query over the network to the SQL Server. (I really thought this does not happen in real life until I saw it one day.) So, what happens in this case? To make things worse, let’s say that the 80kb query text is submitted from the application to the SQL Server at least 100 times per minute, and as often as 300 times per minute in peak times. Here is what happens: in order for this query to reach the SQL Server, it will have to be broken into a of number network packets (according to the packet size settings) – and will travel over the network. On the other side, our SQL Server network card will receive the packets, will pass them to our network layer, the packets will get assembled, and eventually SQL Server will start processing the query – parsing, allegorizing, generating the query execution plan and so on. So far, we have already had a serious network overhead by waiting for the packets to reach our Database Engine. There will certainly be some processing overhead – until the database engine deals with the 80kb query and its 20 subqueries. The waits you see in the DMVs are actually collected from the point the query reaches the SQL Server and the packets are assembled. Let’s say that our query is processed and it finally returns 15000 rows. These rows have a certain size as well, depending on the data types returned. This means that the data will have converted to packages (depending on the network size package settings) and will have to reach the application server. There will also be waits, however, this time you will be able to see a wait type in the DMVs called ASYNC_NETWORK_IO. What this wait type indicates is that the client is not consuming the data fast enough and the network buffers are filling up. Recently Pinal Dave posted a blog on Client Statistics. What Client Statistics does is captures the physical flow characteristics of the query between the client(Management Studio, in this case) and the server and back to the client. As you see in the image, there are three categories: Query Profile Statistics, Network Statistics and Time Statistics. Number of server roundtrips–a roundtrip consists of a request sent to the server and a reply from the server to the client. For example, if your query has three select statements, and they are separated by ‘GO’ command, then there will be three different roundtrips. TDS Packets sent from the client – TDS (tabular data stream) is the language which SQL Server speaks, and in order for applications to communicate with SQL Server, they need to pack the requests in TDS packets. TDS Packets sent from the client is the number of packets sent from the client; in case the request is large, then it may need more buffers, and eventually might even need more server roundtrips. TDS packets received from server –is the TDS packets sent by the server to the client during the query execution. Bytes sent from client – is the volume of the data set to our SQL Server, measured in bytes; i.e. how big of a query we have sent to the SQL Server. This is why it is best to use stored procedures, since the reusable code (which already exists as an object in the SQL Server) will only be called as a name of procedure + parameters, and this will minimize the network pressure. Bytes received from server – is the amount of data the SQL Server has sent to the client, measured in bytes. Depending on the number of rows and the datatypes involved, this number will vary. But still, think about the network load when you request data from SQL Server. Client processing time – is the amount of time spent in milliseconds between the first received response packet and the last received response packet by the client. Wait time on server replies – is the time in milliseconds between the last request packet which left the client and the first response packet which came back from the server to the client. Total execution time – is the sum of client processing time and wait time on server replies (the SQL Server internal processing time) Here is an illustration of the Client-server communication model which should help you understand the mutual waits in a client-server environment. Keep in mind that a query with a large ‘wait time on server replies’ means the server took a long time to produce the very first row. This is usual on queries that have operators that need the entire sub-query to evaluate before they proceed (for example, sort and top operators). However, a query with a very short ‘wait time on server replies’ means that the query was able to return the first row fast. However a long ‘client processing time’ does not necessarily imply the client spent a lot of time processing and the server was blocked waiting on the client. It can simply mean that the server continued to return rows from the result and this is how long it took until the very last row was returned. The bottom line is that developers and DBAs should work together and think carefully of the resource utilization in the client-server environment. From experience I can say that so far I have seen only cases when the application developers and the Database developers are on their own and do not ask questions about the other party’s world. I would recommend using the Client Statistics tool during new development to track the performance of the queries, and also to find a synchronous way of utilizing resources between the client – server – client. Here is another example: think about similar setup as above, but add another server to the game. Let’s say that we keep our media on a separate server, and together with the data from our SQL Server we need to display some images on the webpage requested by our user. No matter how simple or complicated the logic to get the images is, if the images are 500kb each our users will get the page slowly and they will still think that there is something wrong with our data. Anyway, I don’t mean to get carried away too far from SQL Server. Instead, what I would like to say is that DBAs should also be aware of ‘the big picture’. I wrote a blog post a while back on this topic, and if you are interested, you can read it here about the big picture. And finally, here are some guidelines for monitoring the network performance and improving it: Run a trace and outline all queries that return more than 1000 rows (in Profiler you can actually filter and sort the captured trace by number of returned rows). This is not a set number; it is more of a guideline. The general thought is that no application user can consume that many rows at once. Ask yourself and your fellow-developers: ‘why?’. Monitor your network counters in Perfmon: Network Interface:Output queue length, Redirector:Network errors/sec, TCPv4: Segments retransmitted/sec and so on. Make sure to establish a good friendship with your network administrator (buy them coffee, for example J ) and get into a conversation about the network settings. Have them explain to you how the network cards are setup – are they standalone, are they ‘teamed’, what are the settings – full duplex and so on. Find some time to read a bit about networking. In this short blog post I hope I have turned your attention to ‘the big picture’ and the fact that there are other factors affecting our SQL Server, aside from its internal workings. As a further reading I would still highly recommend the Wait Stats series on this blog, also I would recommend you have the coffee break conversation with your network admin as soon as possible. This guest post is written by Feodor Georgiev. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL

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• More CPU cores may not always lead to better performance – MAXDOP and query memory distribution in spotlight

  - by sqlworkshops

  More hardware normally delivers better performance, but there are exceptions where it can hinder performance. Understanding these exceptions and working around it is a major part of SQL Server performance tuning.   When a memory allocating query executes in parallel, SQL Server distributes memory to each task that is executing part of the query in parallel. In our example the sort operator that executes in parallel divides the memory across all tasks assuming even distribution of rows. Common memory allocating queries are that perform Sort and do Hash Match operations like Hash Join or Hash Aggregation or Hash Union.   In reality, how often are column values evenly distributed, think about an example; are employees working for your company distributed evenly across all the Zip codes or mainly concentrated in the headquarters? What happens when you sort result set based on Zip codes? Do all products in the catalog sell equally or are few products hot selling items?   One of my customers tested the below example on a 24 core server with various MAXDOP settings and here are the results:MAXDOP 1: CPU time = 1185 ms, elapsed time = 1188 msMAXDOP 4: CPU time = 1981 ms, elapsed time = 1568 msMAXDOP 8: CPU time = 1918 ms, elapsed time = 1619 msMAXDOP 12: CPU time = 2367 ms, elapsed time = 2258 msMAXDOP 16: CPU time = 2540 ms, elapsed time = 2579 msMAXDOP 20: CPU time = 2470 ms, elapsed time = 2534 msMAXDOP 0: CPU time = 2809 ms, elapsed time = 2721 ms - all 24 cores.In the above test, when the data was evenly distributed, the elapsed time of parallel query was always lower than serial query.   Why does the query get slower and slower with more CPU cores / higher MAXDOP? Maybe you can answer this question after reading the article; let me know: [email protected].   Well you get the point, let’s see an example.   The best way to learn is to practice. To create the below tables and reproduce the behavior, join the mailing list by using this link: www.sqlworkshops.com/ml and I will send you the table creation script.   Let’s update the Employees table with 49 out of 50 employees located in Zip code 2001. update Employees set Zip = EmployeeID / 400 + 1 where EmployeeID % 50 = 1 update Employees set Zip = 2001 where EmployeeID % 50 != 1 go update statistics Employees with fullscan go   Let’s create the temporary table #FireDrill with all possible Zip codes. drop table #FireDrill go create table #FireDrill (Zip int primary key) insert into #FireDrill select distinct Zip from Employees update statistics #FireDrill with fullscan go  Let’s execute the query serially with MAXDOP 1. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --First serially with MAXDOP 1 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 1) goThe query took 1011 ms to complete.   The execution plan shows the 77816 KB of memory was granted while the estimated rows were 799624.  No Sort Warnings in SQL Server Profiler.  Now let’s execute the query in parallel with MAXDOP 0. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --In parallel with MAXDOP 0 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 0) go The query took 1912 ms to complete.  The execution plan shows the 79360 KB of memory was granted while the estimated rows were 799624.  The estimated number of rows between serial and parallel plan are the same. The parallel plan has slightly more memory granted due to additional overhead. Sort properties shows the rows are unevenly distributed over the 4 threads.   Sort Warnings in SQL Server Profiler.   Intermediate Summary: The reason for the higher duration with parallel plan was sort spill. This is due to uneven distribution of employees over Zip codes, especially concentration of 49 out of 50 employees in Zip code 2001. Now let’s update the Employees table and distribute employees evenly across all Zip codes.   update Employees set Zip = EmployeeID / 400 + 1 go update statistics Employees with fullscan go  Let’s execute the query serially with MAXDOP 1. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --Serially with MAXDOP 1 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 1) go   The query took 751 ms to complete.  The execution plan shows the 77816 KB of memory was granted while the estimated rows were 784707.  No Sort Warnings in SQL Server Profiler.   Now let’s execute the query in parallel with MAXDOP 0. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --In parallel with MAXDOP 0 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 0) go The query took 661 ms to complete.  The execution plan shows the 79360 KB of memory was granted while the estimated rows were 784707.  Sort properties shows the rows are evenly distributed over the 4 threads. No Sort Warnings in SQL Server Profiler.    Intermediate Summary: When employees were distributed unevenly, concentrated on 1 Zip code, parallel sort spilled while serial sort performed well without spilling to tempdb. When the employees were distributed evenly across all Zip codes, parallel sort and serial sort did not spill to tempdb. This shows uneven data distribution may affect the performance of some parallel queries negatively. For detailed discussion of memory allocation, refer to webcasts available at www.sqlworkshops.com/webcasts.     Some of you might conclude from the above execution times that parallel query is not faster even when there is no spill. Below you can see when we are joining limited amount of Zip codes, parallel query will be fasted since it can use Bitmap Filtering.   Let’s update the Employees table with 49 out of 50 employees located in Zip code 2001. update Employees set Zip = EmployeeID / 400 + 1 where EmployeeID % 50 = 1 update Employees set Zip = 2001 where EmployeeID % 50 != 1 go update statistics Employees with fullscan go  Let’s create the temporary table #FireDrill with limited Zip codes. drop table #FireDrill go create table #FireDrill (Zip int primary key) insert into #FireDrill select distinct Zip       from Employees where Zip between 1800 and 2001 update statistics #FireDrill with fullscan go  Let’s execute the query serially with MAXDOP 1. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --Serially with MAXDOP 1 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 1) go The query took 989 ms to complete.  The execution plan shows the 77816 KB of memory was granted while the estimated rows were 785594. No Sort Warnings in SQL Server Profiler.  Now let’s execute the query in parallel with MAXDOP 0. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --In parallel with MAXDOP 0 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 0) go The query took 1799 ms to complete.  The execution plan shows the 79360 KB of memory was granted while the estimated rows were 785594.  Sort Warnings in SQL Server Profiler.    The estimated number of rows between serial and parallel plan are the same. The parallel plan has slightly more memory granted due to additional overhead.  Intermediate Summary: The reason for the higher duration with parallel plan even with limited amount of Zip codes was sort spill. This is due to uneven distribution of employees over Zip codes, especially concentration of 49 out of 50 employees in Zip code 2001.   Now let’s update the Employees table and distribute employees evenly across all Zip codes. update Employees set Zip = EmployeeID / 400 + 1 go update statistics Employees with fullscan go Let’s execute the query serially with MAXDOP 1. --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --Serially with MAXDOP 1 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 1) go The query took 250  ms to complete.  The execution plan shows the 9016 KB of memory was granted while the estimated rows were 79973.8.  No Sort Warnings in SQL Server Profiler.  Now let’s execute the query in parallel with MAXDOP 0.  --Example provided by www.sqlworkshops.com --Execute query with uneven Zip code distribution --In parallel with MAXDOP 0 set statistics time on go declare @EmployeeID int, @EmployeeName varchar(48),@zip int select @EmployeeName = e.EmployeeName, @zip = e.Zip from Employees e       inner join #FireDrill fd on (e.Zip = fd.Zip)       order by e.Zip option (maxdop 0) go The query took 85 ms to complete.  The execution plan shows the 13152 KB of memory was granted while the estimated rows were 784707.  No Sort Warnings in SQL Server Profiler.    Here you see, parallel query is much faster than serial query since SQL Server is using Bitmap Filtering to eliminate rows before the hash join.   Parallel queries are very good for performance, but in some cases it can hinder performance. If one identifies the reason for these hindrances, then it is possible to get the best out of parallelism. I covered many aspects of monitoring and tuning parallel queries in webcasts (www.sqlworkshops.com/webcasts) and articles (www.sqlworkshops.com/articles). I suggest you to watch the webcasts and read the articles to better understand how to identify and tune parallel query performance issues.   Summary: One has to avoid sort spill over tempdb and the chances of spills are higher when a query executes in parallel with uneven data distribution. Parallel query brings its own advantage, reduced elapsed time and reduced work with Bitmap Filtering. So it is important to understand how to avoid spills over tempdb and when to execute a query in parallel.   I explain these concepts with detailed examples in my webcasts (www.sqlworkshops.com/webcasts), I recommend you to watch them. The best way to learn is to practice. To create the above tables and reproduce the behavior, join the mailing list at www.sqlworkshops.com/ml and I will send you the relevant SQL Scripts.   Register for the upcoming 3 Day Level 400 Microsoft SQL Server 2008 and SQL Server 2005 Performance Monitoring & Tuning Hands-on Workshop in London, United Kingdom during March 15-17, 2011, click here to register / Microsoft UK TechNet.These are hands-on workshops with a maximum of 12 participants and not lectures. For consulting engagements click here.   Disclaimer and copyright information:This article refers to organizations and products that may be the trademarks or registered trademarks of their various owners. Copyright of this article belongs to R Meyyappan / www.sqlworkshops.com. You may freely use the ideas and concepts discussed in this article with acknowledgement (www.sqlworkshops.com), but you may not claim any of it as your own work. This article is for informational purposes only; you use any of the suggestions given here entirely at your own risk.   Register for the upcoming 3 Day Level 400 Microsoft SQL Server 2008 and SQL Server 2005 Performance Monitoring & Tuning Hands-on Workshop in London, United Kingdom during March 15-17, 2011, click here to register / Microsoft UK TechNet.These are hands-on workshops with a maximum of 12 participants and not lectures. For consulting engagements click here.   R Meyyappan [email protected] LinkedIn: http://at.linkedin.com/in/rmeyyappan  

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• MySQL Query Select using sub-select takes too long

  - by True Soft

  I noticed something strange while executing a select from 2 tables: SELECT * FROM table_1 WHERE id IN ( SELECT id_element FROM table_2 WHERE column_2=3103); This query took approximatively 242 seconds. But when I executed the subquery SELECT id_element FROM table_2 WHERE column_2=3103 it took less than 0.002s (and resulted 2 rows). Then, when I did SELECT * FROM table_1 WHERE id IN (/* prev.result */) it was the same: 0.002s. I was wondering why MySQL is doing the first query like that, taking much more time than the last 2 queries separately? Is it an optimal solution for selecting something based from the results of a sub-query? Other details: table_1 has approx. 9000 rows, and table_2 has 90000 rows. After I added an index on column_2 from table_2, the first query took 0.15s.

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• What's wrong with my MySql query ?!

  - by Anytime

  This is a query I am doing with mysql using PHP This is the query line <?php $query = "SELECT * FROM node WHERE type = 'student_report' AND uid = '{$uid}' LIMIT 1 ORDER BY created DESC"; ?> I get the following error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER BY created DESC' at line 1

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• complex sql which runs extremely slow when the query has order by clause

  - by basit.

  I have following complex query which I need to use. When I run it, it takes 30 to 40 seconds. But if I remove the order by clause, it takes 0.0317 sec to return the result, which is really fast compare to 30 sec or 40. select DISTINCT media.* , username from album as album , album_permission as permission , user as user, media as media where ((media.album_id = album.album_id and album.private = 'yes' and album.album_id = permission.album_id and (permission.email = '' or permission.user_id = '') ) or (media.album_id = album.album_id and album.private = 'no' ) or media.album_id = '0' ) and media.user_id = user.user_id and media.media_type = 'video' order by media.id DESC LIMIT 0,20 The id on order by is primary key which is indexed too. So I don't know what is the problem. I also have album and album permission table, just to check if media is public or private, if private then check if user has permission or not. I was thinking maybe that is causing the issue. What if I did this in sub query, would that work better? Also can someone help me write that sub query, if that is the solution? If you can't help write it, just at least tell me. I'm really going crazy with this issue.. SOLUTION MAYBE Yes, I think sub-query would be best solution for this, because the following query runs at 0.0022 seconds. But I'm not sure if validation of an album would be accurate or not, please check. select media.*, username from media as media , user as user where media.user_id = user.user_id and media.media_type = 'video' and media.id in (select media2.id from media as media2 , album as album , album_permission as permission where ((media2.album_id = album.album_id and album.private = 'yes' and album.album_id = permission.album_id and (permission.email = '' or permission.user_id = '')) or (media.album_id = album.album_id and album.private = 'no' ) or media.album_id = '0' ) and media.album_id = media2.album_id ) order by media.id DESC LIMIT 0,20

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• Specifying a variable name in QUERY WHERE clause in JDBC

  - by Noona

  Could someone please give me a link on how to create a query in JDBC that gets a variable name in the WHERE statement, or write an example, to be more specific, my code looks something like this: private String getLastModified(String url) { String lastModified = null; ResultSet resultSet; String query = "select LastModified from CacheTable where " + " URL.equals(url)"; try { resultSet = sqlStatement.executeQuery(query); } Now I need the syntax that enables me to return a ResultSet object where URL in the cacheTable equals url from the method's argument. thanks

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• SQL select descendants of a row

  - by Joey Adams

  Suppose a tree structure is implemented in SQL like this: CREATE TABLE nodes ( id INTEGER PRIMARY KEY, parent INTEGER -- references nodes(id) ); Although cycles can be created in this representation, let's assume we never let that happen. The table will only store a collection of roots (records where parent is null) and their descendants. The goal is to, given an id of a node on the table, find all nodes that are descendants of it. A is a descendant of B if either A's parent is B or A's parent is a descendant of B. Note the recursive definition. Here is some sample data: INSERT INTO nodes VALUES (1, NULL); INSERT INTO nodes VALUES (2, 1); INSERT INTO nodes VALUES (3, 2); INSERT INTO nodes VALUES (4, 3); INSERT INTO nodes VALUES (5, 3); INSERT INTO nodes VALUES (6, 2); which represents: 1 `-- 2 |-- 3 | |-- 4 | `-- 5 | `-- 6 We can select the (immediate) children of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1; We can select the children and grandchildren of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1 UNION ALL SELECT b.* FROM nodes AS a, nodes AS b WHERE a.parent=1 AND b.parent=a.id; We can select the children, grandchildren, and great grandchildren of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1 UNION ALL SELECT b.* FROM nodes AS a, nodes AS b WHERE a.parent=1 AND b.parent=a.id UNION ALL SELECT c.* FROM nodes AS a, nodes AS b, nodes AS c WHERE a.parent=1 AND b.parent=a.id AND c.parent=b.id; How can a query be constructed that gets all descendants of node 1 rather than those at a finite depth? It seems like I would need to create a recursive query or something. I'd like to know if such a query would be possible using SQLite. However, if this type of query requires features not available in SQLite, I'm curious to know if it can be done in other SQL databases.

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• How to call Named Query

  - by sandeep

  I wrote a named query in the entity class Voter NamedQuery(name = "Voter.findvoter", query = "SELECT count(*) FROM Voter v WHERE v.voterID = :voterID" and where v.password= : password), I want to call this named query and I also need to set voterID and password. Can you help me. Thank you

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• performance issue in a select query from a single table

  - by daedlus

  Hi , I have a table as below dbo.UserLogs ------------------------------------- Id | UserId |Date | Name| P1 | Dirty ------------------------------------- There can be several records per userId[even in millions] I have clustered index on Date column and query this table very frequently in time ranges. The column 'Dirty' is non-nullable and can take either 0 or 1 only so I have no indexes on 'Dirty' I have several millions of records in this table and in one particular case in my application i need to query this table to get all UserId that have at least one record that is marked dirty. I tried this query - select distinct(UserId) from UserLogs where Dirty=1 I have 10 million records in total and this takes like 10min to run and i want this to run much faster than this. [i am able to query this table on date column in less than a minute.] Any comments/suggestion are welcome. my env 64bit,sybase15.0.3,Linux

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• c# linq to xml dynamic query

  - by David Archer

  Right, bit of a strange question; I have been doing some linq to XML work recently (see my other recent posts here and here). Basically, I want to be able to create a query that checks whether a textbox is null before it's value is included in the query, like so: XDocument db = XDocument.Load(xmlPath); var query = (from vals in db.Descendants("Customer") where (if(textbox1.Text != "") {vals.Element("CustomerID") == Convert.ToInt32(textbox1.Text) } || if(textbox2.Text != "") {vals.Element("Name") == textbox2.Text}) select vals).ToList();

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• PostgreSQL - Why are some queries on large datasets so incredibly slow

  - by Brad Mathews

  Hello, I have two types of queries I run often on two large datasets. They run much slower than I would expect them to. The first type is a sequential scan updating all records: Update rcra_sites Set street = regexp_replace(street,'/','','i') rcra_sites has 700,000 records. It takes 22 minutes from pgAdmin! I wrote a vb.net function that loops through each record and sends an update query for each record (yes, 700,000 update queries!) and it runs in less than half the time. Hmmm.... The second type is a simple update with a relation and then a sequential scan: Update rcra_sites as sites Set violations='No' From narcra_monitoring as v Where sites.agencyid=v.agencyid and v.found_violation_flag='N' narcra_monitoring has 1,700,000 records. This takes 8 minutes. The query planner refuses to use my indexes. The query runs much faster if I start with a set enable_seqscan = false;. I would prefer if the query planner would do its job. I have appropriate indexes, I have vacuumed and analyzed. I optimized my shared_buffers and effective_cache_size best I know to use more memory since I have 4GB. My hardware is pretty darn good. I am running v8.4 on Windows 7. Is PostgreSQL just this slow? Or am I still missing something? Thanks! Brad

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• Help me alter this query to get the desired results - New*

  - by sandeepan

  Please dump these data first CREATE TABLE IF NOT EXISTS `all_tag_relations` ( `id_tag_rel` int(10) NOT NULL AUTO_INCREMENT, `id_tag` int(10) unsigned NOT NULL DEFAULT '0', `id_tutor` int(10) DEFAULT NULL, `id_wc` int(10) unsigned DEFAULT NULL, PRIMARY KEY (`id_tag_rel`), KEY `All_Tag_Relations_FKIndex1` (`id_tag`), KEY `id_wc` (`id_wc`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=19 ; INSERT INTO `all_tag_relations` (`id_tag_rel`, `id_tag`, `id_tutor`, `id_wc`) VALUES (1, 1, 1, NULL), (2, 2, 1, NULL), (3, 6, 2, NULL), (4, 7, 2, NULL), (8, 3, 1, 1), (9, 4, 1, 1), (10, 5, 2, 2), (11, 4, 2, 2), (15, 8, 1, 3), (16, 9, 1, 3), (17, 10, 1, 4), (18, 4, 1, 4), (19, 1, 2, 5), (20, 4, 2, 5); CREATE TABLE IF NOT EXISTS `tags` ( `id_tag` int(10) unsigned NOT NULL AUTO_INCREMENT, `tag` varchar(255) DEFAULT NULL, PRIMARY KEY (`id_tag`), UNIQUE KEY `tag` (`tag`), KEY `id_tag` (`id_tag`), KEY `tag_2` (`tag`), KEY `tag_3` (`tag`), KEY `tag_4` (`tag`), FULLTEXT KEY `tag_5` (`tag`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=11 ; INSERT INTO `tags` (`id_tag`, `tag`) VALUES (1, 'Sandeepan'), (2, 'Nath'), (3, 'first'), (4, 'class'), (5, 'new'), (6, 'Bob'), (7, 'Cratchit'), (8, 'more'), (9, 'fresh'), (10, 'second'); CREATE TABLE IF NOT EXISTS `webclasses` ( `id_wc` int(10) NOT NULL AUTO_INCREMENT, `id_author` int(10) NOT NULL, `name` varchar(50) DEFAULT NULL, PRIMARY KEY (`id_wc`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ; INSERT INTO `webclasses` (`id_wc`, `id_author`, `name`) VALUES (1, 1, 'first class'), (2, 2, 'new class'), (3, 1, 'more fresh'), (4, 1, 'second class'), (5, 2, 'sandeepan class'); About the system - The system consists of tutors and classes. - The data in the table All_Tag_Relations stores tag relations for each tutor registered and each class created by a tutor. The tag relations are used for searching classes. The current data dump corresponds to tutor "Sandeepan Nath" who has created classes named "first class", "more fresh", "second class" and tutor "Bob Cratchit" who has created classes "new class" and "Sandeepan class". I am trying for a search query performs AND logic on the search keywords and returns wvery such class for which the search terms are present in the class name or its tutor name To make it easy, following is the list of search terms and desired results:- Search term result classes (check the id_wc in the results) first class 1 Sandeepan Nath class 1 Sandeepan Nath 1,3 Bob Cratchit 2 Sandeepan Nath bob none Sandeepan Class 1,4,5 I have so far reached upto this query -- Two keywords search SET @tag1 = 4, @tag2 = 1; -- Setting some user variables to see where the ids go. SELECT wc.id_wc, sum( DISTINCT ( wtagrels.id_tag = @tag1 ) ) AS key_1_class_matches, sum( DISTINCT ( wtagrels.id_tag = @tag2 ) ) AS key_2_class_matches, sum( DISTINCT ( ttagrels.id_tag = @tag1 ) ) AS key_1_tutor_matches, sum( DISTINCT ( ttagrels.id_tag = @tag2 ) ) AS key_2_tutor_matches, sum( DISTINCT ( ttagrels.id_tag = wtagrels.id_tag ) ) AS key_class_tutor_matches FROM WebClasses as wc join all_tag_relations AS wtagrels on wc.id_wc = wtagrels.id_wc join all_tag_relations as ttagrels on (wc.id_author = ttagrels.id_tutor) WHERE ( wtagrels.id_tag = @tag1 OR wtagrels.id_tag = @tag2 OR ttagrels.id_tag = @tag1 OR ttagrels.id_tag = @tag2 ) GROUP BY wtagrels.id_wc LIMIT 0 , 20 For search with 1 or 3 terms, remove/add the variable part in this query. Tabulating my observation of the values of key_1_class_matches, key_2_class_matches,key_1_tutor_matches (say, class keys),key_2_tutor_matches for various cases (say, tutor keys). Search term expected result Observation first class 1 for class 1, all class keys+all tutor keys =1 Sandeepan Nath class 1 for class 1, one class key+ all tutor keys = 1 Sandeepan Nath 1,3 both tutor keys =1 for these classes Bob Cratchit 2 both tutor keys = 1 Sandeepan Nath bob none no complete tutor matches for any class I found a pattern that, for any case, the class(es) which should appear in the result have the highest number of matches (all class keys and tutor keys). E.g. searching "first class", only for class =1, total of key matches = 4(1+1+1+1) searching "Sandeepan Nath", for classes 1, 3,4(all classes by Sandeepan Nath) have all the tutor keys matching. But no pattern in the search for "Sandeepan Class" - classes 1,4,5 should match. Now, how do I put a condition into the query, based on that pattern so that only those classes are returned. Do I need to use full text search here because it gives a scoring/rank value indicating the strength of the match? Any sample query would help. Please note - I have already found solution for showing classes when any/all of the search terms match with the class name. http://stackoverflow.com/questions/3030022/mysql-help-me-alter-this-search-query-to-get-desired-results But if all the search terms are in tutor name, it does not work. So, I am modifying the query and experimenting.

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• Help me alter this query to get the desired results

  - by sandeepan

  Please dump these data first CREATE TABLE IF NOT EXISTS `all_tag_relations` ( `id_tag_rel` int(10) NOT NULL AUTO_INCREMENT, `id_tag` int(10) unsigned NOT NULL DEFAULT '0', `id_tutor` int(10) DEFAULT NULL, `id_wc` int(10) unsigned DEFAULT NULL, PRIMARY KEY (`id_tag_rel`), KEY `All_Tag_Relations_FKIndex1` (`id_tag`), KEY `id_wc` (`id_wc`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=19 ; INSERT INTO `all_tag_relations` (`id_tag_rel`, `id_tag`, `id_tutor`, `id_wc`) VALUES (1, 1, 1, NULL), (2, 2, 1, NULL), (3, 6, 2, NULL), (4, 7, 2, NULL), (8, 3, 1, 1), (9, 4, 1, 1), (10, 5, 2, 2), (11, 4, 2, 2), (15, 8, 1, 3), (16, 9, 1, 3), (17, 10, 1, 4), (18, 4, 1, 4), (19, 1, 2, 5), (20, 4, 2, 5); CREATE TABLE IF NOT EXISTS `tags` ( `id_tag` int(10) unsigned NOT NULL AUTO_INCREMENT, `tag` varchar(255) DEFAULT NULL, PRIMARY KEY (`id_tag`), UNIQUE KEY `tag` (`tag`), KEY `id_tag` (`id_tag`), KEY `tag_2` (`tag`), KEY `tag_3` (`tag`), KEY `tag_4` (`tag`), FULLTEXT KEY `tag_5` (`tag`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=11 ; INSERT INTO `tags` (`id_tag`, `tag`) VALUES (1, 'Sandeepan'), (2, 'Nath'), (3, 'first'), (4, 'class'), (5, 'new'), (6, 'Bob'), (7, 'Cratchit'), (8, 'more'), (9, 'fresh'), (10, 'second'); CREATE TABLE IF NOT EXISTS `webclasses` ( `id_wc` int(10) NOT NULL AUTO_INCREMENT, `id_author` int(10) NOT NULL, `name` varchar(50) DEFAULT NULL, PRIMARY KEY (`id_wc`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ; INSERT INTO `webclasses` (`id_wc`, `id_author`, `name`) VALUES (1, 1, 'first class'), (2, 2, 'new class'), (3, 1, 'more fresh'), (4, 1, 'second class'), (5, 2, 'sandeepan class'); About the system - The system consists of tutors and classes. - The data in the table All_Tag_Relations stores tag relations for each tutor registered and each class created by a tutor. The tag relations are used for searching classes. The current data dump corresponds to tutor "Sandeepan Nath" who has created classes named "first class", "more fresh", "second class" and tutor "Bob Cratchit" who has created classes "new class" and "Sandeepan class". I am trying for a search query performs AND logic on the search keywords and returns wvery such class for which the search terms are present in the class name or its tutor name To make it easy, following is the list of search terms and desired results:- Search term result classes (check the id_wc in the results) first class 1 Sandeepan Nath class 1 Sandeepan Nath 1,3 Bob Cratchit 2 Sandeepan Nath bob none Sandeepan Class 1,4,5 I have so far reached upto this query -- Two keywords search SET @tag1 = 4, @tag2 = 1; -- Setting some user variables to see where the ids go. SELECT wc.id_wc, sum( DISTINCT ( wtagrels.id_tag = @tag1 ) ) AS key_1_class_matches, sum( DISTINCT ( wtagrels.id_tag = @tag2 ) ) AS key_2_class_matches, sum( DISTINCT ( ttagrels.id_tag = @tag1 ) ) AS key_1_tutor_matches, sum( DISTINCT ( ttagrels.id_tag = @tag2 ) ) AS key_2_tutor_matches, sum( DISTINCT ( ttagrels.id_tag = wtagrels.id_tag ) ) AS key_class_tutor_matches FROM WebClasses as wc join all_tag_relations AS wtagrels on wc.id_wc = wtagrels.id_wc join all_tag_relations as ttagrels on (wc.id_author = ttagrels.id_tutor) WHERE ( wtagrels.id_tag = @tag1 OR wtagrels.id_tag = @tag2 OR ttagrels.id_tag = @tag1 OR ttagrels.id_tag = @tag2 ) GROUP BY wtagrels.id_wc LIMIT 0 , 20 For search with 1 or 3 terms, remove/add the variable part in this query. Tabulating my observation of the values of key_1_class_matches, key_2_class_matches,key_1_tutor_matches (say, class keys),key_2_tutor_matches for various cases (say, tutor keys). Search term expected result Observation first class 1 for class 1, all class keys+all tutor keys =1 Sandeepan Nath class 1 for class 1, one class key+ all tutor keys = 1 Sandeepan Nath 1,3 both tutor keys =1 for these classes Bob Cratchit 2 both tutor keys = 1 Sandeepan Nath bob none no complete tutor matches for any class I found a pattern that, for any case, the class(es) which should appear in the result have the highest number of matches (all class keys and tutor keys). E.g. searching "first class", only for class =1, total of key matches = 4(1+1+1+1) searching "Sandeepan Nath", for classes 1, 3,4(all classes by Sandeepan Nath) have all the tutor keys matching. But no pattern in the search for "Sandeepan Class" - classes 1,4,5 should match. Now, how do I put a condition into the query, based on that pattern so that only those classes are returned. Do I need to use full text search here because it gives a scoring/rank value indicating the strength of the match? Any sample query would help. Please note - I have already found solution for showing classes when any/all of the search terms match with the class name. http://stackoverflow.com/questions/3030022/mysql-help-me-alter-this-search-query-to-get-desired-results But if all the search terms are in tutor name, it does not work. So, I am modifying the query and experimenting.

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• Iterating result of Select Query

  - by user294146

  Hi experts, I have a question related to select query. here i am explaining down below. i have a table with the following data **Column1(Primary Key) Column2 Column3** ------ --------- -------------- 1 C 2 C 3 Null 4 H 5 L 6 H my problem is i have to replace the value of Column3 with the corresponding value of Column1 for every occurrence of data "C", "H" and "L". Please provide me query related to this problem. how can i solve this using query or stored procedure. please elaborate the same. I need final select query result as follows **Column1(Primary Key) Column2 Column3** ------ --------- -------------- 1 C 1 2 C 2 3 Null 4 H 4 5 L 5 6 H 6 Thanks & Regards, Murali

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• Help with linq to sql compiled query

  - by stackoverflowuser

  Hi I am trying to use compiled query for one of my linq to sql queries. This query contains 5 to 6 joins. I was able to create the compiled query but the issue I am facing is my query needs to check if the key is within a collection of keys passed as input. But compiled queries do not allow passing of collection (since collection can have varying number of items hence not allowed). For instance input to the function is a collection of keys. Say: List<Guid> InputKeys List<SomeClass> output = null; var compiledQuery = CompiledQueries.Compile<DataContext, IQueryable<SomeClass>>( (context) => from a in context.GetTable<A>() where InputKeys.Contains(a.Key) select a); using(var dataContext = new DataContext()) { output = compiledQuery(dataContext).ToList(); } return output; Is there any work around or better way to do the above?

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• Mysql - help me optimize this query

  - by sandeepan-nath

  About the system: -The system has a total of 8 tables - Users - Tutor_Details (Tutors are a type of User,Tutor_Details table is linked to Users) - learning_packs, (stores packs created by tutors) - learning_packs_tag_relations, (holds tag relations meant for search) - tutors_tag_relations and tags and orders (containing purchase details of tutor's packs), order_details linked to orders and tutor_details. For a more clear idea about the tables involved please check the The tables section in the end. -A tags based search approach is being followed.Tag relations are created when new tutors register and when tutors create packs (this makes tutors and packs searcheable). For details please check the section How tags work in this system? below. Following is a simpler representation (not the actual) of the more complex query which I am trying to optimize:- I have used statements like explanation of parts in the query select SUM(DISTINCT( t.tag LIKE "%Dictatorship%" )) as key_1_total_matches, SUM(DISTINCT( t.tag LIKE "%democracy%" )) as key_2_total_matches, td., u., count(distinct(od.id_od)), if (lp.id_lp > 0) then some conditional logic on lp fields else 0 as tutor_popularity from Tutor_Details AS td JOIN Users as u on u.id_user = td.id_user LEFT JOIN Learning_Packs_Tag_Relations AS lptagrels ON td.id_tutor = lptagrels.id_tutor LEFT JOIN Learning_Packs AS lp ON lptagrels.id_lp = lp.id_lp LEFT JOIN `some other tables on lp.id_lp - let's call learning pack tables set (including Learning_Packs table)` LEFT JOIN Order_Details as od on td.id_tutor = od.id_author LEFT JOIN Orders as o on od.id_order = o.id_order LEFT JOIN Tutors_Tag_Relations as ttagrels ON td.id_tutor = ttagrels.id_tutor JOIN Tags as t on (t.id_tag = ttagrels.id_tag) OR (t.id_tag = lptagrels.id_tag) where some condition on Users table's fields AND CASE WHEN ((t.id_tag = lptagrels.id_tag) AND (lp.id_lp 0)) THEN `some conditions on learning pack tables set` ELSE 1 END AND CASE WHEN ((t.id_tag = wtagrels.id_tag) AND (wc.id_wc 0)) THEN `some conditions on webclasses tables set` ELSE 1 END AND CASE WHEN (od.id_od0) THEN od.id_author = td.id_tutor and some conditions on Orders table's fields ELSE 1 END AND ( t.tag LIKE "%Dictatorship%" OR t.tag LIKE "%democracy%") group by td.id_tutor HAVING key_1_total_matches = 1 AND key_2_total_matches = 1 order by tutor_popularity desc, u.surname asc, u.name asc limit 0,20 ===================================================================== What does the above query do? Does AND logic search on the search keywords (2 in this example - "Democracy" and "Dictatorship"). Returns only those tutors for which both the keywords are present in the union of the two sets - tutors details and details of all the packs created by a tutor. To make things clear - Suppose a Tutor name "Sandeepan Nath" has created a pack "My first pack", then:- Searching "Sandeepan Nath" returns Sandeepan Nath. Searching "Sandeepan first" returns Sandeepan Nath. Searching "Sandeepan second" does not return Sandeepan Nath. ====================================================================================== The problem The results returned by the above query are correct (AND logic working as per expectation), but the time taken by the query on heavily loaded databases is like 25 seconds as against normal query timings of the order of 0.005 - 0.0002 seconds, which makes it totally unusable. It is possible that some of the delay is being caused because all the possible fields have not yet been indexed, but I would appreciate a better query as a solution, optimized as much as possible, displaying the same results ========================================================================================== How tags work in this system? When a tutor registers, tags are entered and tag relations are created with respect to tutor's details like name, surname etc. When a Tutors create packs, again tags are entered and tag relations are created with respect to pack's details like pack name, description etc. tag relations for tutors stored in tutors_tag_relations and those for packs stored in learning_packs_tag_relations. All individual tags are stored in tags table. ==================================================================== The tables Most of the following tables contain many other fields which I have omitted here. CREATE TABLE IF NOT EXISTS users ( id_user int(10) unsigned NOT NULL AUTO_INCREMENT, name varchar(100) NOT NULL DEFAULT '', surname varchar(155) NOT NULL DEFAULT '', PRIMARY KEY (id_user) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=636 ; CREATE TABLE IF NOT EXISTS tutor_details ( id_tutor int(10) NOT NULL AUTO_INCREMENT, id_user int(10) NOT NULL DEFAULT '0', PRIMARY KEY (id_tutor), KEY Users_FKIndex1 (id_user) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=51 ; CREATE TABLE IF NOT EXISTS orders ( id_order int(10) unsigned NOT NULL AUTO_INCREMENT, PRIMARY KEY (id_order), KEY Orders_FKIndex1 (id_user), ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=275 ; ALTER TABLE orders ADD CONSTRAINT Orders_ibfk_1 FOREIGN KEY (id_user) REFERENCES users (id_user) ON DELETE NO ACTION ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS order_details ( id_od int(10) unsigned NOT NULL AUTO_INCREMENT, id_order int(10) unsigned NOT NULL DEFAULT '0', id_author int(10) NOT NULL DEFAULT '0', PRIMARY KEY (id_od), KEY Order_Details_FKIndex1 (id_order) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=284 ; ALTER TABLE order_details ADD CONSTRAINT Order_Details_ibfk_1 FOREIGN KEY (id_order) REFERENCES orders (id_order) ON DELETE NO ACTION ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS learning_packs ( id_lp int(10) unsigned NOT NULL AUTO_INCREMENT, id_author int(10) unsigned NOT NULL DEFAULT '0', PRIMARY KEY (id_lp), KEY Learning_Packs_FKIndex2 (id_author), KEY id_lp (id_lp) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=23 ; CREATE TABLE IF NOT EXISTS tags ( id_tag int(10) unsigned NOT NULL AUTO_INCREMENT, tag varchar(255) DEFAULT NULL, PRIMARY KEY (id_tag), UNIQUE KEY tag (tag), KEY id_tag (id_tag), KEY tag_2 (tag), KEY tag_3 (tag) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3419 ; CREATE TABLE IF NOT EXISTS tutors_tag_relations ( id_tag int(10) unsigned NOT NULL DEFAULT '0', id_tutor int(10) DEFAULT NULL, KEY Tutors_Tag_Relations (id_tag), KEY id_tutor (id_tutor), KEY id_tag (id_tag) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; ALTER TABLE tutors_tag_relations ADD CONSTRAINT Tutors_Tag_Relations_ibfk_1 FOREIGN KEY (id_tag) REFERENCES tags (id_tag) ON DELETE NO ACTION ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS learning_packs_tag_relations ( id_tag int(10) unsigned NOT NULL DEFAULT '0', id_tutor int(10) DEFAULT NULL, id_lp int(10) unsigned DEFAULT NULL, KEY Learning_Packs_Tag_Relations_FKIndex1 (id_tag), KEY id_lp (id_lp), KEY id_tag (id_tag) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; ALTER TABLE learning_packs_tag_relations ADD CONSTRAINT Learning_Packs_Tag_Relations_ibfk_1 FOREIGN KEY (id_tag) REFERENCES tags (id_tag) ON DELETE NO ACTION ON UPDATE NO ACTION; =================================================================================== Following is the exact query (this includes classes also - tutors can create classes and search terms are matched with classes created by tutors):- select count(distinct(od.id_od)) as tutor_popularity, CASE WHEN (IF((wc.id_wc 0), ( wc.wc_api_status = 1 AND wc.wc_type = 0 AND wc.class_date '2010-06-01 22:00:56' AND wccp.status = 1 AND (wccp.country_code='IE' or wccp.country_code IN ('INT'))), 0)) THEN 1 ELSE 0 END as 'classes_published', CASE WHEN (IF((lp.id_lp 0), (lp.id_status = 1 AND lp.published = 1 AND lpcp.status = 1 AND (lpcp.country_code='IE' or lpcp.country_code IN ('INT'))),0)) THEN 1 ELSE 0 END as 'packs_published', td . * , u . * from Tutor_Details AS td JOIN Users as u on u.id_user = td.id_user LEFT JOIN Learning_Packs_Tag_Relations AS lptagrels ON td.id_tutor = lptagrels.id_tutor LEFT JOIN Learning_Packs AS lp ON lptagrels.id_lp = lp.id_lp LEFT JOIN Learning_Packs_Categories AS lpc ON lpc.id_lp_cat = lp.id_lp_cat LEFT JOIN Learning_Packs_Categories AS lpcp ON lpcp.id_lp_cat = lpc.id_parent LEFT JOIN Learning_Pack_Content as lpct on (lp.id_lp = lpct.id_lp) LEFT JOIN Webclasses_Tag_Relations AS wtagrels ON td.id_tutor = wtagrels.id_tutor LEFT JOIN WebClasses AS wc ON wtagrels.id_wc = wc.id_wc LEFT JOIN Learning_Packs_Categories AS wcc ON wcc.id_lp_cat = wc.id_wp_cat LEFT JOIN Learning_Packs_Categories AS wccp ON wccp.id_lp_cat = wcc.id_parent LEFT JOIN Order_Details as od on td.id_tutor = od.id_author LEFT JOIN Orders as o on od.id_order = o.id_order LEFT JOIN Tutors_Tag_Relations as ttagrels ON td.id_tutor = ttagrels.id_tutor JOIN Tags as t on (t.id_tag = ttagrels.id_tag) OR (t.id_tag = lptagrels.id_tag) OR (t.id_tag = wtagrels.id_tag) where (u.country='IE' or u.country IN ('INT')) AND CASE WHEN ((t.id_tag = lptagrels.id_tag) AND (lp.id_lp 0)) THEN lp.id_status = 1 AND lp.published = 1 AND lpcp.status = 1 AND (lpcp.country_code='IE' or lpcp.country_code IN ('INT')) ELSE 1 END AND CASE WHEN ((t.id_tag = wtagrels.id_tag) AND (wc.id_wc 0)) THEN wc.wc_api_status = 1 AND wc.wc_type = 0 AND wc.class_date '2010-06-01 22:00:56' AND wccp.status = 1 AND (wccp.country_code='IE' or wccp.country_code IN ('INT')) ELSE 1 END AND CASE WHEN (od.id_od0) THEN od.id_author = td.id_tutor and o.order_status = 'paid' and CASE WHEN (od.id_wc 0) THEN od.can_attend_class=1 ELSE 1 END ELSE 1 END AND 1 group by td.id_tutor order by tutor_popularity desc, u.surname asc, u.name asc limit 0,20 Please note - The provided database structure does not show all the fields and tables as in this query

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• Ampersand in sqlite query

  - by Denis Gorodetskiy

  How to construct sqlite query containing ampersand in filter: SELECT id FROM mediainfo WHERE album="Betty & Kate"; I use sqlite C interface (sqlite3_bind_text() and ? marks while query building) but neither C query nor SQLite Administrator return any data

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• Recursively MySQL Query

  - by Rachel

  How can I implement recursive MySQL Queries. I am trying to look for it but resources are not very helpful. Trying to implement similar logic. public function initiateInserts() { //Open Large CSV File(min 100K rows) for parsing. $this->fin = fopen($file,'r') or die('Cannot open file'); //Parsing Large CSV file to get data and initiate insertion into schema. $query = ""; while (($data=fgetcsv($this->fin,5000,";"))!==FALSE) { $query = $query + "INSERT INTO dt_table (id, code, connectid, connectcode) VALUES (" + $data[0] + ", " + $data[1] + ", " + $data[2] + ", " + $data[3] + ")"; } $stmt = $this->prepare($query); // Execute the statement $stmt->execute(); $this->checkForErrors($stmt); } @Author: Numenor Error Message: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '0' at line 1 This Approach inspired to look for an MySQL recursive query approach.

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• mysql query optimisation

  - by Bharanikumar

  i have around (1,049,906 total, Query took 0.0005 sec) in my x table , If i simply retrieve trying to retrive the particular field records , Its tooks hardly 6 mins , This is my query SELECT CUSTOMER_CODE FROM X_TBL ; CUSTOMER_CODE = UNIQUE THE ABOVE QUERY TOOK 6MIN , Tel me optimization tips for this , Also in some situation to search customer , i used the CUSTOMER_CODE in like , select CUSTOMER_CODE from X_TBL WHERE CUSTOMER_CODE LIKE "$KEY_WORD%" Regards Bharanikumar

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• Passing Multiple values Through Query String?

  - by Googler

  Hi all, I tried to pass more than one value through Query String from page1.aspx to page2.aspx. This is my Query string in the Grid View <a href="javascript:void(0);" onclick='javascript:window.open("Update.aspx?Regno= <%#Eval ("ID") %>'+ ","'&Fn=<%#Eval ("FIRSTNAME") %>' +", "'&Ln=<%#Eval ("LASTNAME") %>'")';> Edit</a> On My Page2.aspx, my code behind on PageLoad is: if (Page.IsPostBack) return; string id = Request.QueryString["ID"]; string Firstname = Request.QueryString["FIRSTNAME"]; string LastName = Request.QueryString["LASTNAME"]; My Visual Studio IDE shows a syntax error on this query string. I dont know the exact way to pass multiple values through Query String. How to make it work? Can anyone pls help me on this.. Which is the right syntax to pass multiple query string?

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• Using the LIMIT statement in a SQLite query

  - by anselmophil

  Hi guys. I have a query that selects rows in a ListView without having a limit. But now that i have implemented a SharedPreferences that the user can select how much rows will be displayed in the ListView, my SQLite query doesnt work. Im passing the argument this way: return wDb.query(TABELANOME, new String[] {IDTIT, TAREFATIT, SUMARIOTIT}, CONCLUIDOTIT + "=1", null, null, null, null, "LIMIT='" + limite + "'"); Help, please!

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• MySQL database query returns empty result

  - by user1791096

  I am doing a data migration and getting empty result of simple query with one join. Following is the query Select * from users u INNER JOIN temp_users tu ON tu.uid = u.uid There hundreds of records which have same uid in both tables, but this query returns only one record. Following is the structure of tables users table uid: varchar(50) utf8_general_ci Yes NULL temp_users table uid: varchar(50) utf8_general_ci Yes NULL Is there anyone who faced same problem?

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• Rails - Trying to query from a date range...everything from today

  - by ChrisWesAllen

  I'm trying to figure the best way to query a date range from rails...I looked around on Google but am unsure about how to use this syntax. I have a Model that has various events and I like to add to my find condition a caveat that should only show events where the field :st_date is today or later, in effect only show me data that is current, nothing that happened before today. I ran into a problem because I have no end date to stop the query, I want to query everything from today to next month. I was thinking something like @events = Event.find(:all, :conditions => ["start_date between ? and ?", date.Today, date.next_month.beginning_of_month]) but I get the error undefined local variable or method `date'...... Do I need do anything particular to use the Date class? Or is there something wrong with my query syntax? I would really appreciate any help.

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• SQL Query in NHibernate diction

  - by Jan-Frederik Carl

  I have a SQL Query which works in SQL Management Studio: Select Id From table t Where t.Date= (Select Max(Date) From ( Select * From table where ReferenceId = xy) u) Reason is, from all entries with a certain foreign key, I want to receive the one with the highest date. I tried to reform this Query for use in NHibernate, and I got IQuery query = session.CreateQuery(String.Format( @"Select t.Id From table t Where t.Date = (Select Max(Date) From (Select * From table t where t.ReferenceItem.Id = " + item.ReferenceItem.Id + ")u)")); I get the error message: "In expected" How do I have to form the NHibernate query? What does the "In" mean?

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• How to extract the Sql Command from a Complied Linq Query

  - by Harry

  In normal (not compiled) Linq to Sql queries you can extract the SQLCommand from the IQueryable via the following code: SqlCommand cmd = (SqlCommand)table.Context.GetCommand(query); Is it possible to do the same for a compiled query? The following code provides me with a delegate to a compiled query: private static readonly Func<Data.DAL.Context, string, IQueryable<Word>> Query_Get = CompiledQuery.Compile<Data.DAL.Context, string, IQueryable<Word>>( (context, name) => from r in context.GetTable<Word>() where r.Name == name select r); When i use this to generate the IQueryable and attempt to extract the SqlCommand it doesn't seem to work. When debugging the code I can see that the SqlCommand returned has the 'very' useful CommandText of 'SELECT NULL AS [EMPTY]' using (var db = new Data.DAL.Context()) { IQueryable<Word> query = Query_Get(db, "word"); SqlCommand cmd = (SqlCommand)db.GetCommand(query); Console.WriteLine(cmd != null ? cmd.CommandText : "Command Not Found"); } I can't find anything in google about this particular scenario, as no doubt it is not a common thing to attempt... So.... Any thoughts?

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