query-optimization

问题 Using EXPLAIN reveals that the following query does not use my index, could somebody please explain what is going on? SELECT u.id AS userId, firstName, profilePhotoId, preferredActivityId, preferredSubActivityId, availabilityType, 3959 * ACOS(COS(radians(requestingUserLat)) * COS(radians(u.latitude)) * COS(radians(u.longitude) - radians(requestingUserLon)) + SIN(radians(requestingUserLat)) * SIN(radians(u.latitude))) AS distanceInMiles FROM users u WHERE u.latitude between lat1 and lat2 --

问题 I migrated a MySQL database from one environment to another, and discovered that after migrating, a particular query runs extremely slower than it was. I was investigating the statement with 'explain' keyword (below) and found that the 'explain' command gives different output, on different servers. explain select distinct j.job,f.path,p.path from fixes f join jobs j on f.job=j.id join paths p on p.id =f.path where p.path like '//depot1/Dev\-trunk/%' ; For the original one, it gives: 1 SIMPLE

问题 I'm writing a query like this: select * from myTable where X in (select X from Y) and XX in (select X from Y) Values from columns X and XX has to be in the result of the same query: select X from Y . I think that this query is invoked twice so its senseless. Is there any other option I can write this query more efficiently? Maybe temp table? 回答1: Actually no, there isn't a smarter way to write this (without visiting Y twice) given the X that myTable.X and myTable.YY matches to may not be from

问题 I have a trace table which looks like this I'd like to get a running total which looks like the following output - its very important that I retain the order - as this is the execution order of the stored porcedures - It will help me analyze bottle necks in the system I have tried select max(RowNumber),objectname, count(1) from rob where eventclass = 42 group by objectname But that mucks up the order Is this even possible in SQL? UPDATE: I tried this select RowNumber,objectname, count(1) from

问题 I have a table like the following: user | item ------------- X | Apple X | Orange X | Pear Y | Orange Y | Pear Z | Apple Z | Orange My goal is to have 3 search options: ANY , ALL (At Least), EXACT Where ANY returns a list of users who have at least one item searched for, so searching for "Apple" - ANY would return X,Z, searching for "Apple, Orange" - ANY would return X,Y,Z ALL returns a list of users who have all items searched for, so searching for "Apple" - ALL would return X,Z, searching

问题 Is there an alternate way to pass node elements dynamically than the one shown below - ? select XMLTable.XMLCOL.query('//*[local-name()=sql:variable("@node")') For e.g., even if I am trying to give the fully qualified path, I do not want to hard code the node elements, instead I would like to pass them individually as parameters. Under the section - Example: Query Using sp_executesql @ http://msdn.microsoft.com/en-us/library/ms345118(v=sql.90).aspx it says - query contains wildcards (*) and

问题 I've got a table structure that can be summarized as follows: pagegroup * pagegroupid * name has 3600 rows page * pageid * pagegroupid * data references pagegroup; has 10000 rows; can have anything between 1-700 rows per pagegroup; the data column is of type mediumtext and the column contains 100k - 200kbytes data per row userdata * userdataid * pageid * column1 * column2 * column9 references page; has about 300,000 rows; can have about 1-50 rows per page The above structure is pretty

问题 I'm trying to offer a feature where I can show pages most viewed by friends. My friends table has 5.7M rows and the views table has 5.3M rows. At the moment I just want to run a query on these two tables and find the 20 most viewed page id's by a person's friend. Here's the query as I have it now: SELECT page_id FROM `views` INNER JOIN `friendships` ON friendships.receiver_id = views.user_id WHERE (`friendships`.`creator_id` = 143416) GROUP BY page_id ORDER BY count(views.user_id) desc LIMIT

问题 I have a SQL that can be simplified to: SELECT * FROM table WHERE LOCATE( column, :keyword ) > 0 ORDER BY LOCATE( column, :keyword ) You can see there is a duplicate of "LOCATE( column, :keyword )". Is there a way to calculate it only once ? 回答1: HAVING works with aliases in MySQL: SELECT *, LOCATE( column, :keyword ) AS somelabel FROM table HAVING somelabel > 0 ORDER BY somelabel 回答2: SELECT *, LOCATE( column, :keyword ) AS somelabel FROM table WHERE somelabel > 0 ORDER BY somelabel 回答3:

问题 I'm currently running a DELETE query that is taking a lot longer than expected (already 10hrs!). I would like to kill it through phpmyadmin processes, however am concerned about what might happen. Will the roll-back he automatically does take a lot of time also? Current query status shows "updating". 回答1: It depends on the stage your query is in right now. But generally rollback takes about equal time, sometimes even more than the original operation. As per point 2 of this document, it's not