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  • Get smallest date for each element in access query

    - by skerit
    So I have a table containing different elements and dates. It basically looks like this: actieElement beginDatum 1 1/01/2010 1 1/01/2010 1 10/01/2010 2 1/02/2010 2 3/02/2010 What I now need is the smallest date for every actieElement. I've found a solution using a simple GROUP BY statement, but that way the query loses its scope and you can't change anything anymore. Without the GROUP BY statement I get multiple dates for every actieElement because certain dates are the same. I thought of something like this, but it also does not work as it would give the subquery more then 1 record: SELECT s1.actieElement, s1.begindatum FROM tblActieElementLink AS s1 WHERE (((s1.actieElement)=(SELECT TOP 1 (s2.actieElement) FROM tblActieElementLink s2 WHERE s1.actieElement = s2.actieElement ORDER BY s2.begindatum ASC)));

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  • getting rid of repeated customer id's in mysql query

    - by bsandrabr
    I originally started by selecting customers from a group of customers and then for each customer querying the records for the past few days and presenting them in a table row. All working fine but I think I might have got too ambitious as I tried to pull in all the records at once having heard that mutiple queries are a big no no. here is the mysqlquery i came up with to pull in all the records at once SELECT morning, afternoon, date, date2, fname, lname, customers.customerid FROM customers LEFT OUTER JOIN attend ON ( customers.customerid = attend.customerid ) RIGHT OUTER JOIN noattend ON ( noattend.date2 = attend.date ) WHERE noattend.date2 BETWEEN '$date2' AND '$date3' AND DayOfWeek( date2 ) %7 >1 AND group ={$_GET['group']} ORDER BY lname ASC , fname ASC , date2 DESC tables are customer-customerid,fname,lname attend-customerid,morning,afternoon,date noattend-date2 (a table of all the days to fill in the blanks) Now the problem I have is how to start a new row in the table when the customer id changes My query above pulls in customer 1 morning 2 customer 1 morning 1 customer 2 morning 2 customer 2 morning 1 whereas I'm trying to get customer1 morning2 morning1 customer2 morning2 morning1 I dont know whether this is possible in the sql or more likely in the php

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  • How can I use an array within a SQL query

    - by ThinkingInBits
    So I'm trying to take a search string (could be any number of words) and turn each value into a list to use in the following IN statement) in addition, I need a count of all these values to use with my having count filter $search_array = explode(" ",$this->search_string); $tag_count = count($search_array); $db = Connect::connect(); $query = "select p.id from photographs p left join photograph_tags c on p.id = c.photograph_id and c.value IN ($search_array) group by p.id having count(c.value) >= $tag_count"; This currently returns no results, any ideas?

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  • CASE + IF MysQL query

    - by terence6
    Problem is as follows. I have a product that can be in one of three categories (defined by category_id). Each category table has category_id field related to category_id in product table. So I have 3 cases. I'm checking If my product.category_id is in table one. If yes, I take some values. If not I check in tables that are left. What can I write In the ELSE section? Can anyone correct my query ? CASE WHEN IF EXISTS(SELECT * FROM table1 WHERE category_id='category_id') THEN SELECT type_id FROM table1 WHERE category_id='category_id'; WHEN IF EXISTS(SELECT * FROM table2 WHERE category_id='category_id') THEN SELECT value_id FROM table2 WHERE category_id='category_id'; WHEN IF EXISTS(SELECT * FROM table3 WHERE category_id='category_id') THEN SELECT group_id FROM table3 WHERE category_id='category_id'; ELSE "dont know what here"; END;

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  • Query - Trying to SUM one field based on content of another field

    - by ShaneL
    Table: DayOfWeek Enrollments Monday 35 Monday 12 Saturday 25 Tuesday 15 Monday 9 Tuesday 15 Basically I'm trying to sum the total enrolments for each day. so the Output will look like: DayOfWeek Enrollments Monday 56 Saturday 25 Tuesday 30 I've spent around 4 hours trying to work this out trying many many different ways but no luck. The problem I'm having is i can count how many enrollments for each day but can't have it aligned with the correct day when i run the query e.g. I want The total to be on the same line as the day it was calculated from. (I hope that is clear enough)

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  • Help constructing query - Compare columns and replace numbers

    - by Tommy
    I have a feeling that this query is pretty easy to construct, I just can't figure it out. I want to replace all numbers in table X column C, with numbers in table Z column A, where numbers from table X column C matches numbers in table Z column B. I hope that makes sense. Perhaps a little background information will make it clearer. I've converted from one CMS to another, and the module I used to convert mapped the ids to the new database. Table X column A is the new id's. Table X column B is the old id's. Table Z is the table for an image gallery that I migrated, and column C contains the id's of the images owners. Can anyone crack this nut?

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  • SQL query help - merge a value to all rows in a column

    - by Tommy
    I'm trying to migrate a site from a joomla system to a drupal. The problem is that drupal needs filename and sourcepath in the same row, but joomla only has filename. I'm looking for a way to add sourcepath before the filename in all the rows in that column. I'm figuring it's the UPDATE statement that I should use, but I can't figure out how to construct the query. There's a person with a similar problem here, but I don't find the answers in that thread helpful to my problem: http://www.daniweb.com/forums/showth...t+value&page=2 Any suggestions?

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  • MySQL query problem

    - by SaltLake
    I've got MySQL table CREATE TABLE stat ( ID int NOT NULL auto_increment PRIMARY KEY, TIMESTAMP_X timestamp DEFAULT CURRENT_TIMESTAMP, # ... some other fields ... ) which contains statistics about site visitors. For getting visits per hour I use SELECT hour(TIMESTAMP_X) as HOUR , count(*) AS HOUR_STAT FROM cms_webstat GROUP BY HOUR ORDER BY HOUR DESC which gives me | HOUR | HOUR_STAT | | 24 | 15 | | 23 | 12 | | 22 | 9 | | 20 | 3 | | 18 | 2 | | 15 | 1 | | 12 | 3 | | 9 | 1 | | 3 | 5 | | 2 | 7 | | 1 | 9 | | 0 | 12 | And I'd like to get following: | HOUR | HOUR_STAT | | 24 | 15 | | 23 | 12 | | 22 | 9 | | 21 | 0 | | 20 | 3 | | 19 | 0 | | 18 | 2 | | 17 | 0 | | 16 | 0 | | 15 | 1 | | 14 | 0 | | 13 | 0 | | 12 | 3 | | 11 | 0 | | 10 | 0 | | 9 | 1 | | 8 | 0 | | 7 | 0 | | 6 | 0 | | 5 | 0 | | 4 | 0 | | 3 | 5 | | 2 | 7 | | 1 | 9 | | 0 | 12 | How should I modify the query to get such result? Thanks.

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  • Sql-server Database query help

    - by menacheb
    Hi, I have a problem that I didn't manage to solve for a very long time, and I quite desperate. I have a Database (SQL Server) with table named 'ProcessData' and columns named 'Process_Name' (Data Type: nvarchar(50)), 'Start_At' (DataType: DateTime) and 'End_At' (Data Type: DateTime). I need to know for each 'Time-Interval' (let's say 1 minute) how many processes (Process_Name = PN) was open (after or equal to the 'Start_at' column and before or equal to the 'End_At' column) during this time (It can be a few rows with the same data). Does anyone know how to make this query without a 'for' loop? (It ITSELF will promote the time), (The answer will be a table with two columns (1. The time the check took place. 2. the number of open processes at this time.) and a row for each 'Time-Interval' (1 minute in this example ) Many thanks,

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  • Need help with some complex SQL query

    - by Psyche
    Hello guys, I need some help with a complex SQL query. Here's my setup: there are two tables, one with authors, and another with books. The books table contains a field named "author" which holds author's id. If a book has more than one author, then the "author" field will contain all the authors ids separated by ";" (something like 2;34;234). On the website I have to list all the books written by an author. If there's only one author, its simple, but how can I get those books where the author I'm interested in is the second or third author? Many thanks.

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  • Django query - join on the same table

    - by dana
    i have a mini blog app, and a 'timeline' . there i want to be displayed all the posts from all the friends of a user, plus the posts of that user himself. For that, i have to make some kind of a 'join' between the results of two queries (queries on the same table) , so that the final result will be the combination of the user - posesor of the account, and all his friends. My query looks like this: blog = New.objects.filter(created_by = following,created_by = request.user) By that ',' i wanted to make a 'join' -i found something like this on a doc- but this method is not correct- i'm getting an error. How else could be done this 'join' ? Thanks!

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  • sql query is too slow, how to improve speed

    - by user1289282
    I have run into a bottleneck when trying to update one of my tables. The player table has, among other things, id, skill, school, weight. What I am trying to do is: SELECT id, skill FROM player WHERE player.school = (current school of 4500) AND player.weight = (current weight of 14) to find the highest skill of all players returned from the query UPDATE player SET starter = 'TRUE' WHERE id = (highest skill) move to next weight and repeat when all weights have been completed move to next school and start over all schools completed, done I have this code implemented and it works, but I have approximately 4500 schools totaling 172000 players and the way I have it now, it would take probably a half hour or more to complete (did not wait it out), which is way too slow. How to speed this up? Short of reducing the scale of the system, I am willing to do anything that gets the intended result. Thanks! *the weights are the standard folk style wrestling weights ie, 103, 113, 120, 126, 132, 138, 145, 152, 160, 170, 182, 195, 220, 285 pounds

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  • Counting multiple rows in MySQL in one query

    - by diggersworld
    I currently have a table which stores a load of statistics such as views, downloads, purchases etc. for a multiple number of items. To get a single operation count on each item I can use the following query: SELECT , COUNT() FROM stats WHERE operation = 'view' GROUP BY item_id This gives me all the items and a count of their views. I can then change 'view' to 'purchase' or 'download' for the other variables. However this means three separate calls to the database. Is it possible to get all three in one go?

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  • Update query (access & vb.net)

    - by yae
    Hi: I have to update some fields of a table of access according to the value of parameter. If this paramter is "true" I need to update. Table idInvoice price percentageTax1 tax1 percentageTax2 tax2 total Example values: idinvoice: 12300 price: 100 € percentageTax1: 10 % tax1= 10€ percentageTax2: 5 % tax2: 5€ total: 115 € (result: 100€+10€+5€) Ok. If the parameter on that I have commented before is "true" I must update the percentages and then update the total. I need to replace the "old" percentages by new percent. Ok I can do it in 3 queries: update invocies set percentageTax1=20,tax1=price *(percentageTax1/100) where idInvoice=@number and percentageTax1=10 update invocies set percentageTax2=7,tax2=price *(percentageTax2/100) where idInvoice=@number and percentageTax2=5 update invocies set total=price+tax1+tax2 where idInvoice=@number . But my question is: is there any an alternative to do this in 1 query?

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  • [SQL][MS access] Query to find duplicate item in 2 table

    - by Rico
    I have this table Antecedent Consequent I1 I2 I1 I1,I2,I3 I1 I4,I1,I3,I4 I1,I2 I1 I1,I2 I1,I4 I1,I2 I1,I3 I1,I4 I3,I2 I1,I2,I3 I1,I4 I1,I3,I4 I4 AS you can see it's pretty messed up. is there anyway i can remove rows if item in consequent exist in antecedent (in 1 row) for example: INPUT: Antecedent Consequent I1 I2 I1 I1,I2,I3 <---- DELETE since I1 exist in antecedent I1 I4,I1,I3,I4 <---- DELETE since I1 exist in antecedent I1,I2 I1 <---- DELETE since I1 exist in antecedent I1,I2 I1,I4 <---- DELETE since I1 exist in antecedent I1,I2 I1,I3 <---- DELETE since I1 exist in antecedent I1,I4 I3,I2 <---- DELETE since I2 exist in antecedent I1,I2,I3 I1,I4 I1,I3,I4 I4 <---- DELETE since I4 exist in antecedent OUTPUT: Antecedent Consequent I1 I2 I1,I2,I3 I1,I4 is there anyway i can do that by query?

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  • INSERT DELAYED on locked tables blocks PHP processes to continue

    - by sw0x2A
    Our webservers write some tracking information into a MySQL database (using INSERT DELAYED into MyISAM table). When a huge SELECT query is executed on this table or when it is locked for another reason, the webserver processes (with INSERT DELAYED) are waiting for the database and in some cases the MaxServer limit is reached in Apaches, so they will stop serving requests. We use INSERT DELAYED because The DELAYED option for the INSERT statement is a MySQL extension to standard SQL that is very useful if you have clients that cannot or need not wait for the INSERT to complete. This is a common situation when you use MySQL for logging and you also periodically run SELECT and UPDATE statements that take a long time to complete. Quote from MySQL documentation. I am wondering why the Apache processes are waiting for the INSERT DELAYED to finish. And what can I do to just send the data and forget about it. (Since this is logging data, I do not care if we lose some entries.) Even when the table is locked the PHP script should just go on and should not wait for an answer of MySQL. (We do not want to setup Master-slave for this table but we are thinking about move this data to some NoSQL database. But for now I would like to know why INSERT DELAYED is not working as expected.)

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  • SQL SERVER – Subquery or Join – Various Options – SQL Server Engine knows the Best

    - by pinaldave
    This is followup post of my earlier article SQL SERVER – Convert IN to EXISTS – Performance Talk, after reading all the comments I have received I felt that I could write more on the same subject to clear few things out. First let us run following four queries, all of them are giving exactly same resultset. USE AdventureWorks GO -- use of = SELECT * FROM HumanResources.Employee E WHERE E.EmployeeID = ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA WHERE EA.EmployeeID = E.EmployeeID) GO -- use of in SELECT * FROM HumanResources.Employee E WHERE E.EmployeeID IN ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA WHERE EA.EmployeeID = E.EmployeeID) GO -- use of exists SELECT * FROM HumanResources.Employee E WHERE EXISTS ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA WHERE EA.EmployeeID = E.EmployeeID) GO -- Use of Join SELECT * FROM HumanResources.Employee E INNER JOIN HumanResources.EmployeeAddress EA ON E.EmployeeID = EA.EmployeeID GO Let us compare the execution plan of the queries listed above. Click on image to see larger image. It is quite clear from the execution plan that in case of IN, EXISTS and JOIN SQL Server Engines is smart enough to figure out what is the best optimal plan of Merge Join for the same query and execute the same. However, in the case of use of Equal (=) Operator, SQL Server is forced to use Nested Loop and test each result of the inner query and compare to outer query, leading to cut the performance. Please note that here I no mean suggesting that Nested Loop is bad or Merge Join is better. This can very well vary on your machine and amount of resources available on your computer. When I see Equal (=) operator used in query like above, I usually recommend to see if user can use IN or EXISTS or JOIN. As I said, this can very much vary on different system. What is your take in above query? I believe SQL Server Engines is usually pretty smart to figure out what is ideal execution plan and use it. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Joins, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Subquery or Join – Various Options – SQL Server Engine Knows the Best – Part 2

    - by pinaldave
    This blog post is part 2 of the earlier written article SQL SERVER – Subquery or Join – Various Options – SQL Server Engine knows the Best by Paulo R. Pereira. Paulo has left excellent comment to earlier article once again proving the point that SQL Server Engine is smart enough to figure out the best plan itself and uses the same for the query. Let us go over his comment as he has posted. “I think IN or EXISTS is the best choice, because there is a little difference between ‘Merge Join’ of query with JOIN (Inner Join) and the others options (Left Semi Join), and JOIN can give more results than IN or EXISTS if the relationship is 1:0..N and not 1:0..1. And if I try use NOT IN and NOT EXISTS the query plan is different from LEFT JOIN too (Left Anti Semi Join vs. Left Outer Join + Filter). So, I found a case where EXISTS has a different query plan than IN or ANY/SOME:” USE AdventureWorks GO -- use of SOME SELECT * FROM HumanResources.Employee E WHERE E.EmployeeID = SOME ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA UNION ALL SELECT EA.EmployeeID FROM HumanResources.EmployeeDepartmentHistory EA ) -- use of IN SELECT * FROM HumanResources.Employee E WHERE E.EmployeeID IN ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA UNION ALL SELECT EA.EmployeeID FROM HumanResources.EmployeeDepartmentHistory EA ) -- use of EXISTS SELECT * FROM HumanResources.Employee E WHERE EXISTS ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA UNION ALL SELECT EA.EmployeeID FROM HumanResources.EmployeeDepartmentHistory EA ) When looked into execution plan of the queries listed above indeed we do get different plans for queries and SQL Server Engines creates the best (least cost) plan for each query. Click on image to see larger images. Thanks Paulo for your wonderful contribution. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Contribution, SQL, SQL Authority, SQL Joins, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Stored Procedure and Transactions

    - by pinaldave
    I just overheard the following statement – “I do not use Transactions in SQL as I use Stored Procedure“. I just realized that there are so many misconceptions about this subject. Transactions has nothing to do with Stored Procedures. Let me demonstrate that with a simple example. USE tempdb GO -- Create 3 Test Tables CREATE TABLE TABLE1 (ID INT); CREATE TABLE TABLE2 (ID INT); CREATE TABLE TABLE3 (ID INT); GO -- Create SP CREATE PROCEDURE TestSP AS INSERT INTO TABLE1 (ID) VALUES (1) INSERT INTO TABLE2 (ID) VALUES ('a') INSERT INTO TABLE3 (ID) VALUES (3) GO -- Execute SP -- SP will error out EXEC TestSP GO -- Check the Values in Table SELECT * FROM TABLE1; SELECT * FROM TABLE2; SELECT * FROM TABLE3; GO Now, the main point is: If Stored Procedure is transactional then, it should roll back complete transactions when it encounters any errors. Well, that does not happen in this case, which proves that Stored Procedure does not only provide just the transactional feature to a batch of T-SQL. Let’s see the result very quickly. It is very clear that there were entries in table1 which are not shown in the subsequent tables. If SP was transactional in terms of T-SQL Query Batches, there would be no entries in any of the tables. If you want to use Transactions with Stored Procedure, wrap the code around with BEGIN TRAN and COMMIT TRAN. The example is as following. CREATE PROCEDURE TestSPTran AS BEGIN TRAN INSERT INTO TABLE1 (ID) VALUES (11) INSERT INTO TABLE2 (ID) VALUES ('b') INSERT INTO TABLE3 (ID) VALUES (33) COMMIT GO -- Execute SP EXEC TestSPTran GO -- Check the Values in Tables SELECT * FROM TABLE1; SELECT * FROM TABLE2; SELECT * FROM TABLE3; GO -- Clean up DROP TABLE Table1 DROP TABLE Table2 DROP TABLE Table3 GO In this case, there will be no entries in any part of the table. What is your opinion about this blog post? Please leave your comments about it here. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Stored Procedure, SQL Tips and Tricks, T SQL, Technology

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  • Modify Wordpress SQL Query to pull from within a category

    - by Levi
    Hi I am using a wordpress plugin called "kf most read" which stores a count of how many times a post was read, and lets you output a list of most read posts. This works well. The issue is, I am trying to pull the most read posts, but only the most read posts within the current category you are viewing. I am close to clueless when it comes to sql. Here us what the plugin is currently using to pull the most read posts: $sql = "SELECT count(mr.post_ID) as totHits, p.ID, p.post_title from $wpdb-posts p JOIN {$wpdb-prefix}kf_most_read mr on mr.post_ID = p.ID where mr.hit_ts = '".(time() - ( 86400 * $period))."' GROUP BY mr.post_ID order by totHits desc, ID ASC LIMIT $limit"; How could I incorporate the below query which pulls from a specific category into the above? $sql .= "LEFT JOIN $wpdb-term_taxonomy ON($wpdb-term_relationships.term_taxonomy_id = $wpdb-term_taxonomy.term_taxonomy_id)" ; $sql .= "WHERE $wpdb-term_taxonomy.term_id IN ($currentcat)" ; $sql .= "AND $wpdb-term_taxonomy.taxonomy = 'category'" ; Any Help on this would be much appreciated.

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  • Help Converting T-SQL Query to LINQ Query

    - by campbelt
    I am new to LINQ, and so am struggle over some queries that I'm sure are pretty simple. In any case, I have been hiting my head against this for a while, but I'm stumped. Can anyone here help me convert this T-SQL query into a LINQ query? Once I see how it is done, I'm sure I'll have some question about the syntax: SELECT BlogTitle FROM Blogs b JOIN BlogComments bc ON b.BlogID = bc.BlogID WHERE b.Deleted = 0 AND b.Draft = 0 AND b.[Default] = 0 AND bc.Deleted = 0 GROUP BY BlogTitle ORDER BY MAX([bc].[Timestamp]) DESC Just to show that I have tried to solve this on my own, here is what I've come up with so far, though it doesn't compile, let alone work ... var iqueryable = from blog in db.Blogs join blogComment in db.BlogComments on blog.BlogID equals blogComment.BlogID where blog.Deleted == false && blog.Draft == false && blog.Default == false && blogComment.Deleted == false group blogComment by blog.BlogID into blogGroup orderby blogGroup.Max(blogComment => blogComment.Timestamp) select blogGroup;

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  • In SQL Server can I insert multiple nodes into XML from a table?

    - by tpower
    I want to generate some XML in a stored procedure based on data in a table. The following insert allows me to add many nodes but they have to be hard-coded or use variables (sql:variable): SET @MyXml.modify(' insert <myNode> {sql:variable("@MyVariable")} </myNode> into (/root[1]) ') So I could loop through each record in my table, put the values I need into variables and execute the above statement. But is there a way I can do this by just combining with a select statement and avoiding the loop? Edit I have used SELECT FOR XML to do similar stuff before but I always find it hard to read when working with a hierarchy of data from multiple tables. I was hoping there would be something using the modify where the XML generated is more explicit and more controllable.

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  • Slow MySQL Query Breaking my back!

    - by Chris n
    so, I have tried everything I can think of, and can't get this query to happen in less than 3 seconds on my local server. I know the problem has to do with the OR referencing both the owner_id and the person_id. if I run one or the other it happens instantly, but together with an or I can't seem to make it work - I looked into rewriting the code, but the way the app was designed it won't be easy. is there a way I can call an equivalent or that won't take so long? here is the sql: SELECT event_types.name as event_type_name,event_types.id as id, count(events.id) as count,sum(events.estimated_duration) as time_sum FROM events,event_types WHERE event_types.id = events.event_type_id AND events.event_type_id != '4' AND ( events.status!='cancelled') AND events.event_type_id != 64 AND ( events.owner_id = 161 OR events.person_id = 161 ) GROUP BY event_types.name ORDER BY event_types.name DESC; Here's the Explain soup, although I'm guessing it's unnecessary cause there is probably a better way to structure that or that is obvious: thanks so much! chris. +----+-------------+-------------+-------+---------------------------------------------------------------------------------------------------------+-------------------------------+---------+-------------------------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------------+-------+---------------------------------------------------------------------------------------------------------+-------------------------------+-- | 1 | SIMPLE | event_types | range | PRIMARY | PRIMARY | 4 | NULL | 78 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | events | ref | index_events_on_status,index_events_on_event_type_id,index_events_on_person_id,index_events_on_owner_id | index_events_on_event_type_id | 5 | thenumber_production.event_types.id | 907 | Using where | +----+-------------+-------------+-------+---------------------------------------------------------------------------------------------------------+-------------------------------+---------+-------------------------------------+------+----------------------------------------------+

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  • Command-Query-Separation and multithreading safe interfaces

    - by Tobias Langner
    I like the command query separation pattern (from OOSC / Eiffel - basically you either return a value or you change the state of the class - but not both). This makes reasoning about the class easier and it is easier to write exception safe classes. Now, with multi threading, I run into a major problem: the separation of the query and the command basically invalidates the result from the query as anything can happen between those 2. So my question is: how do you handle command query separation in an multi-threaded environment? Clarification example: A stack with command query separation would have the following methods: push (command) pop (command - but does not return a value) top (query - returns the value) empty (query) The problem here is - I can get empty as status, but then I can not rely on top really retrieving an element since between the call of empty and the call of top, the stack might have been emptied. Same goes for pop & top. If I get an item using top, I can not be sure that the item that I pop is the same. This can be solved using external locks - but that's not exactly what I call threadsafe design.

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