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  • How do you think while formulating Sql Queries. Is it an experience or a concept ?

    - by Shantanu Gupta
    I have been working on sql server and front end coding and have usually faced problem formulating queries. I do understand most of the concepts of sql that are needed in formulating queries but whenever some new functionality comes into the picture that can be dont using sql query, i do usually fails resolving them. I am very comfortable with select queries using joins and all such things but when it comes to DML operation i usually fails For every query that i never done before I usually finds uncomfortable with that while creating them. Whenever I goes for an interview I usually faces this problem. Is it their some concept behind approaching on formulating sql queries. Eg. I need to create an sql query such that A table contain single column having duplicate record. I need to remove duplicate records. I know i can find the solution to this query very easily on Googling, but I want to know how everyone comes to the desired result. Is it something like Practice Makes Man Perfect i.e. once you did it, next time you will be able to formulate or their is some logic or concept behind. I could have get my answer of solving above problem simply by posting it on stackoverflow and i would have been with an answer within 5 to 10 minutes but I want to know the reason. How do you work on any new kind of query. Is it a major contribution of experience or some an implementation of concepts. Whenever I learns some new thing in coding section I tries to utilize it wherever I can use it. But here scenario seems to be changed because might be i am lagging in some concepts.

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  • wordpress generating slow mysql queries - is it index problem?

    - by tash
    Hello Stack Overflow I've got very slow Mysql queries coming up from my wordpress site. It's making everything slow and I think this is eating up CPU usage. I've pasted the Explain results for the two most frequently problematic queries below. This is a typical result - although very occasionally teh queries do seem to be performed at a more normal speed. I have the usual wordpress indexes on the database tables. You will see that one of the queries is generated from wordpress core code, and not from anything specific - like the theme - for my site. I have a vague feeling that the database is not always using the indexes/is not using them properly... Is this right? Does anyone know how to fix it? Or is it a different problem entirely? Many thanks in advance for any help anyone can offer - it is hugely appreciated Query: [wp-blog-header.php(14): wp()] SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 6 id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE wp_posts ref type_status_date type_status_date 63 const 427 Using where; Using filesort Query time: 34.2829 (ms) 9) Query: [wp-content/themes/LMHR/index.php(40): query_posts()] SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.ID NOT IN ( SELECT tr.object_id FROM wp_term_relationships AS tr INNER JOIN wp_term_taxonomy AS tt ON tr.term_taxonomy_id = tt.term_taxonomy_id WHERE tt.taxonomy = 'category' AND tt.term_id IN ('217', '218', '223', '224') ) AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 6 id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY wp_posts ref type_status_date type_status_date 63 const 427 Using where; Using filesort 2 DEPENDENT SUBQUERY tr ref PRIMARY,term_taxonomy_id PRIMARY 8 func 1 Using index 2 DEPENDENT SUBQUERY tt eq_ref PRIMARY,term_id_taxonomy,taxonomy PRIMARY 8 antin1_lovemusic2010.tr.term_taxonomy_id 1 Using where Query time: 70.3900 (ms)

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  • How Best to Replace Ugly Queries and Dynamic PL/SQL with C#?

    - by Mike
    Hi, I write a lot of one-off Oracle SQL queries (in Toad), and sometimes they can get complex, involving lots of unions, joins, and subqueries, and sometimes requiring dynamic SQL. That is, sometimes SQL queries require set based processing along with significant procedural processing. This is what PL/SQL is custom made for, but as a language it does not begin to compare to C#. Now and then I convert a PL/SQL procedure to C#, and am always amazed at how much cleaner and easier to both read and write the C# version is. The C# program might for example construct a SQL query string piece by piece and/or run several queries and process them as needed. The C# version is usually much faster as well, which must mean that I'm not very good at PL/SQL either. I do not currently have access to LINQ. My question is, how best to package all these little C# programs, which are really just mini reports, that is, replacements for ugly SQL queries? Right now I'm actually using NUnit to hold them, and calling each report a [Test], even though they aren't really tests. NUnit just happens to provide a convenient packaging framework.

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  • How can I make PHP scripts timeout gracefully while waiting for long-running MySQL queries?

    - by Mark B
    I have a PHP site which runs quite a lot of database queries. With certain combinations of parameters, these queries can end up running for a long time, triggering an ugly timeout message. I want to replace this with a nice timeout message themed according to the rest of my site style. Anticipating the usual answers to this kind of question: "Optimise your queries so they don't run for so long" - I am logging long-running queries and optimising them, but I only know about these after a user has been affected. "Increase your PHP timeout setting (e.g. set_time_limit, max_execution_time) so that the long-running query can finish" - Sometimes the query can run for several minutes. I want to tell the user there's a problem before that (e.g. after 30 seconds). "Use register_tick_function to monitor how long scripts have been running" - This only gets executed between lines of code in my script. While the script is waiting for a response from the database, the tick function doesn't get called. In case it helps, the site is built using Drupal (with lots of customisation), and is running on a virtual dedicated Linux server on PHP 5.2 with MySQL 5.

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  • mysql 5.1 - innodb - query_cache_size - 9,418,108 queries have been removed from the query cache due to lack of memory

    - by Tom C
    Currently running on a 16GB system - Ubuntu 64 bit. INnodb Buffer Pool is set to 10GB. tuning-primer shows the following: QUERY CACHE Query cache is enabled Current query_cache_size = 512 M Current query_cache_used = 501 M Current query_cache_limit = 4 M Current Query cache Memory fill ratio = 97.87 % Current query_cache_min_res_unit = 4 K However, 9418108 queries have been removed from the query cache due to lack of memory Perhaps you should raise query_cache_size That is over 9million queries removed. System uptime is 8 days. Should I remove the Query Cache altogether? Our db is always under heavy I/O. tia

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  • How to log slow queries in shared hosting MySQL?

    - by tomaszs
    I have a shared hosting where I have my website and MySQL database. I've installed a open source script for statistics (phpMyVisites) and it started to work very slow lately. It's written using some kind of framework and has many PHP files. I know that to find slow queries I can use slow query log functionality in MySQL. But on this shared hosting I can not use this method because I can not change my.cnf. I don't want to change my statistics script to other and I don't want to mess around with all files of this script to find out where to put diagnostics code to log queries manually. I would like to do it without changes in PHP code. So my question is: How to log slow queries in these coditions?: Can't change my.cnf to enable slow query log Can't change statistics script to other Don't know how scrpt is written and where mysql commands are issued Can't ask my provider for slow query log Is there any method to do this in simple, easy, fast way?

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  • How many SQL queries per HTTP request is optimal?

    - by Chris Kooken
    I know the answer to this question for the most part is "It Depends", however I wanted to see if anyone had some pointers. We execute queries each request in ASP.NET MVC. Each request we need to get user rights information, and Various data for the Views that we are displaying. How many is too much, I know I should be conscious to the number of queries i am executing. I would assume if they are small queries and optimized out, half-a-dozen should be okay? Am I right? What do you think?

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  • MySql multiple selects batching in .net

    - by Amith George
    I have a situation in my application. For each x-axis point in my chart, I am plotting 5 y-axis values. To calculate each of these 5 values, I need to make 4 different queries. Ie, for each x-axis point I need to fire 20 sql queries. Now, I need to plot 40 such points in the my chart. Its resulting in a pathetic performance where it takes close to a minute to get all the data back from the database. Each of 4 different queries consists of a join between 2 tables. One has only 6 rows. The other close to 10,000. Each of the 4 queries has different WHERE clauses, so they are different queries. For each point in the x-axis, only the values for the where clauses change. I have tried combining each of the 4 queries into one big string. Basically batch the four selects. These are again batched for each y-axis value. So, for each x-axis point, I am now firing one big command that consists of 20 different select statements. Technically, I should be experiencing a big performance boost, right? Instead of hitting the db 40x5x4 = 800 times, I am now hitting it just 40 times. But instead of taking 60 seconds, it taking 50-55 seconds... not much of a help. I am using MySql 5.1, and the 6.1 version of its .Net connector. What can I do to improve the performance? Edit: One of the 4 queries is as follows: SELECT SUM(TIME_TO_SEC(TIMEDIFF(T1.col2, T1.col1))* T2.col1 / (3600 *1000)) AS TotalTime FROM Table T1 JOIN Table T2 ON T1.col3 = T2.col3 WHERE T1.col4 = 'i' AND T1.col1 >= '2009-12-25 00:00:00' AND T1.col2 <= '2009-12-26 00:00:00'; The other 3 queries are similar, only the where clause changes slightly. This set of 4 queries is fired 5 times. The first 3 times against the join of table T1 and T2, passing in different values for col4. And the next two times against the join of table T3 and T2 passing in different values for col4. These 5 values are the y-axis values for a particular x-axis point. The data returned by all these queries is the same format. so, we tried doing a UNION ALL on all these queries. No substantial difference. One strange thing, however, after indexing the foreign key on the table T1 [while it contained over a lakh records], the queries were using the index, but they had become slower. At times, the queries would take double the time to return the data.

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  • Secret of SQL Trace Duration Column

    - by Dan Guzman
    Why would a trace of long-running queries not show all queries that exceeded the specified duration filter?  We have a server-side SQL Trace that includes RPC:Completed and SQL:BatchCompleted events with a filter on Duration >= 100000.  Nearly all of the queries on this busy OLTP server run in under this 100 millisecond threshold so any that appear in the trace are candidates for root cause analysis and/or performance tuning opportunities. After an application experienced query timeouts, the DBA looked at the trace data to corroborate the problem.  Surprisingly, he found no long-running queries in the trace from the application that experienced the timeouts even though the application’s error log clearly showed detail of the problem (query text, duration, start time, etc.).  The trace did show, however, that there were hundreds of other long-running queries from different applications during the problem timeframe.  We later determined those queries were blocked by a large UPDATE query against a critical table that was inadvertently run during this busy period. So why didn’t the trace include all of the long-running queries?  The reason is because the SQL Trace event duration doesn’t include the time a request was queued while awaiting a worker thread.  Remember that the server was under considerable stress at the time due to the severe blocking episode.  Most of the worker threads were in use by blocked queries and new requests were queued awaiting a worker to free up (a DMV query on the DAC connection will show this queuing: “SELECT scheduler_id, work_queue_count FROM sys.dm_os_schedulers;”).  Technically, those queued requests had not started.  As worker threads became available, queries were dequeued and completed quickly.  These weren’t included in the trace because the duration was under the 100ms duration filter.  The duration reflected the time it took to actually run the query but didn’t include the time queued waiting for a worker thread. The important point here is that duration is not end-to-end response time.  Duration of RPC:Completed and SQL:BatchCompleted events doesn’t include time before a worker thread is assigned nor does it include the time required to return the last result buffer to the client.  In other words, duration only includes time after the worker thread is assigned until the last buffer is filled.  But be aware that duration does include the time need to return intermediate result set buffers back to the client, which is a factor when large query results are returned.  Clients that are slow in consuming results sets can increase the duration value reported by the trace “completed” events.

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  • Are there any modeling tools that can visually generate jpa or sql queries?

    - by Shervin
    Does anyone know of a tool like PowerArchitect or SquirrelSQL or maybe eclipse plugin that lets you also generate jpa/sql queries? Imagine you choosing your database, or your entity beans, and the modeling would reverse engineer your database/entity model, so that you could visually just choose the columns you wanted to select, and it would generate jpa or sql queries for you. For instance choosing A.b and X.y would generate something like this: select a.b, x.y from A a, X x join ......

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  • How Can I Log and Find the Most Expensive Queries?

    - by Pure.Krome
    Hi folks The activity monitor in sql2k8 allows us to see the most expensive queries. Ok, that's kewl, but is there a way I can log this info or get this info via query analyser? I don't really want to have the Sql Management console open and me looking at the activity monitor dashboard. I want to figure out which queries are poorly written/schema is poorly designed, etc. Thanks heaps for any help!

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  • Is it necessary to write ROLLBACK if queries fail?

    - by Donator
    I write mysql_query("SET AUTOCOMMIT=0"); mysql_query("START TRANSACTION"); before I write all queries. Then check if all of them are true and then write: mysql_query("COMMIT"); But if one of query fails, I just pass COMMIT query. So do I really need ROLLBACK function if one of the queries fail? Because without ROLLBACK it also works. Thanks.

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  • Append Results from two queries and output as a single table.

    - by tHeSiD
    I have two queries that I have to run, I cannon join them But their resultant tables have the same structrure. For example I have select * from products where producttype=magazine select * from products where producttype = book I have to combine the result of these two queries, and then output it as one single result. I have to do this inside a stored procedure. PS These are just examples I provided, i have a complex table structure. The main thing is I cannot join them.

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  • SQLAuthority News Were sorry but your computer or network may be sending automated queries. To pro

    I use multiple browser many times when I am working with multiple projects simultaneously. Often I use Google Reader to read few feeds. Recently, I faced the following error and this error will not go. I even restarted my computer and rebooted my network. I am confident that my computer does not have viruses or [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Using ADO.NET Entities LINQ Provider to model complex SQL Queries?

    - by Ivan Zlatanov
    What I find really powerful in ADO.NET Entities or LINQ to SQL, is the ability to model complex queries. I really don't need the mappings that Entities or LINQ to SQL are doing for me - I just need the ability to model complex expressions that can be translated into T-SQL. My question is - am I abusing too much? Can I use the Entity Framework for modeling queries and just that? Should I? I know I can write my own custom LINQ to SQL provider, but that is just not possible to handle in the time spans I have. What is the best approach to model complex T-SQL queries? How do you handle conditional group byes, orders, joins, unions etc in the OOP world? Using StringBuilders for this kind of job feels too ugly and harder to maintain given the possibilities we have with Expression Trees. When I use StringBuilder to model a complex SQL Query I feel kind of guilty! I feel the same way as when I have to hard code any number into my code that is different than 0 or 1. Feeling that makes you ask yourself if there is a better and cleaner way of doing it... I must mention that I am using C# 4.0, but I am not specifically looking for an answer in this language, but rather in the domain of CLR 4.

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  • Why are .local and .arpa DNS queries showing up outside my network on OpenDNS?

    - by Baodad
    We have a Windows office network with a local Actice Directory/DNS domain server. The server is set up with OpenDNS's servers as forwarders (see screenshot). However, when I look at my OpenDNS query statistics, I notice that the 3rd most popular query is *.in-addr-arpa, and the 12th is *.local which is from our local domain. Should I, or how can I prevent these local queries from going beyond my local network?

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  • Is there a system monitoring tool that lets me write complex queries against the data?

    - by benhsu
    I am looking for a system stat collection tool that will let me write queries against the data collected. I am planning to answer questions like: what is the average load, over the last 30 days, on this machine between 9AM and 5PM, as opposed to at night what was the average disk io on these 10 machines yesterday what was the average daytime memory usage on these 10 machines last week, as opposed to 2 weeks ago Has anyone done this with, say, collectd or graphite?

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  • SPARC T4-4 Delivers World Record Performance on Oracle OLAP Perf Version 2 Benchmark

    - by Brian
    Oracle's SPARC T4-4 server delivered world record performance with subsecond response time on the Oracle OLAP Perf Version 2 benchmark using Oracle Database 11g Release 2 running on Oracle Solaris 11. The SPARC T4-4 server achieved throughput of 430,000 cube-queries/hour with an average response time of 0.85 seconds and the median response time of 0.43 seconds. This was achieved by using only 60% of the available CPU resources leaving plenty of headroom for future growth. The SPARC T4-4 server operated on an Oracle OLAP cube with a 4 billion row fact table of sales data containing 4 dimensions. This represents as many as 90 quintillion aggregate rows (90 followed by 18 zeros). Performance Landscape Oracle OLAP Perf Version 2 Benchmark 4 Billion Fact Table Rows System Queries/hour Users* Response Time (sec) Average Median SPARC T4-4 430,000 7,300 0.85 0.43 * Users - the supported number of users with a given think time of 60 seconds Configuration Summary and Results Hardware Configuration: SPARC T4-4 server with 4 x SPARC T4 processors, 3.0 GHz 1 TB memory Data Storage 1 x Sun Fire X4275 (using COMSTAR) 2 x Sun Storage F5100 Flash Array (each with 80 FMODs) Redo Storage 1 x Sun Fire X4275 (using COMSTAR with 8 HDD) Software Configuration: Oracle Solaris 11 11/11 Oracle Database 11g Release 2 (11.2.0.3) with Oracle OLAP option Benchmark Description The Oracle OLAP Perf Version 2 benchmark is a workload designed to demonstrate and stress the Oracle OLAP product's core features of fast query, fast update, and rich calculations on a multi-dimensional model to support enhanced Data Warehousing. The bulk of the benchmark entails running a number of concurrent users, each issuing typical multidimensional queries against an Oracle OLAP cube consisting of a number of years of sales data with fully pre-computed aggregations. The cube has four dimensions: time, product, customer, and channel. Each query user issues approximately 150 different queries. One query chain may ask for total sales in a particular region (e.g South America) for a particular time period (e.g. Q4 of 2010) followed by additional queries which drill down into sales for individual countries (e.g. Chile, Peru, etc.) with further queries drilling down into individual stores, etc. Another query chain may ask for yearly comparisons of total sales for some product category (e.g. major household appliances) and then issue further queries drilling down into particular products (e.g. refrigerators, stoves. etc.), particular regions, particular customers, etc. Results from version 2 of the benchmark are not comparable with version 1. The primary difference is the type of queries along with the query mix. Key Points and Best Practices Since typical BI users are often likely to issue similar queries, with different constants in the where clauses, setting the init.ora prameter "cursor_sharing" to "force" will provide for additional query throughput and a larger number of potential users. Except for this setting, together with making full use of available memory, out of the box performance for the OLAP Perf workload should provide results similar to what is reported here. For a given number of query users with zero think time, the main measured metrics are the average query response time, the median query response time, and the query throughput. A derived metric is the maximum number of users the system can support achieving the measured response time assuming some non-zero think time. The calculation of the maximum number of users follows from the well-known response-time law N = (rt + tt) * tp where rt is the average response time, tt is the think time and tp is the measured throughput. Setting tt to 60 seconds, rt to 0.85 seconds and tp to 119.44 queries/sec (430,000 queries/hour), the above formula shows that the T4-4 server will support 7,300 concurrent users with a think time of 60 seconds and an average response time of 0.85 seconds. For more information see chapter 3 from the book "Quantitative System Performance" cited below. -- See Also Quantitative System Performance Computer System Analysis Using Queueing Network Models Edward D. Lazowska, John Zahorjan, G. Scott Graham, Kenneth C. Sevcik external local Oracle Database 11g – Oracle OLAP oracle.com OTN SPARC T4-4 Server oracle.com OTN Oracle Solaris oracle.com OTN Oracle Database 11g Release 2 oracle.com OTN Disclosure Statement Copyright 2012, Oracle and/or its affiliates. All rights reserved. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners. Results as of 11/2/2012.

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