query-optimization

问题 This is related to Why is SQLite refusing to use available indexes? The queries to create the database is: CREATE TABLE foo(id TEXT); CREATE INDEX `foo.index` ON foo(id); CREATE TABLE bar(id TEXT); CREATE INDEX `bar.index` ON bar(id); CREATE VIEW baz AS SELECT id FROM foo UNION ALL SELECT id FROM bar; CREATE TABLE bam(id TEXT, value TEXT); INSERT INTO foo VALUES('123'); INSERT INTO foo VALUES('1123'); INSERT INTO foo VALUES('2123'); INSERT INTO foo VALUES('3123'); INSERT INTO bar VALUES(

问题 I have a Query like below select id,name,baseid,member_card_type,membercard_num,last_draw,counter from details_dest where datediff(curdate(),basedate)<100; i have used the explain on that and found it is using index which is on basedate and i think date_diff is the problem so please suggest me is there any other way to execute it without any functions and kindly tell me which is better datediff() or to_days() in according to performance i am using mysql 5.5 回答1: I would suggest the following

问题 This is just a prospective question, at work we're thinking of moving from SQL Server to PostgreSQL, please tell me I didn't understand this correctly from the PostgreSQL 9.4 documentation: "There is no plan caching for commands executed via EXECUTE". We have a critical SP that builds a dynamic query and executes it, initially I didn't build the dynamic SQL correctly (the dynamic query was not parameterized) and because of that each time when this SP was hit, it spend ~ 1500ms to recompile

问题 I am profiling some MS SQL queries with the SQL Server Profiler for my C# Application that I develop with Visual Studio and IIS Express: The duration that is given for the event "Audit Logout" (16876 ms) is the total time between login and logout. The duration for the query is only 60 ms. Login/Logout events are related to the setting up / tearing down. From What is "Audit Logout" in SQL Server Profiler? I would like to understand the time difference of 16816 ms (= 16876 ms - 60ms) in more

问题 Each time I save() a new domain object in Grails I see Hibernate issuing Select statements for each of the unique constraints in my Grails domain class. If I save without validation, I don't see the Select statements. Example: new Person(name: 'Foo').save(validate: false) Is there a way to stop these extra Select statements from occurring while still having validation enabled? One of my goals is to decrease appserver/database chattiness since I am expecting my Grails app to run on a high

问题 long time lurker, first question! I am struggling to optimize this query, which selects the lowest priced items that match the chosen filters: SELECT product_info.*, MIN(product_all.sale_price) as sale_price, product_all.buy_link FROM product_info NATURAL JOIN (SELECT * FROM product_all WHERE product_all.date = '2010-09-30') as product_all WHERE (product_info.category = 2 AND product_info.gender = 'W' ) GROUP BY product_all.prod_id ORDER BY MIN(product_all.sale_price) ASC LIMIT 13 Its explain

问题 Is there anyway to prioritize or throttle a query at all in MySQL? I'm a DBA on a server that sees a lot of unoptimized queries come into the server and they just destroy the CPU. I'm looking at throttling certain users that hit on the database in poor fashion. Clarification: I realize that MySQL has facilities built in to limit number of queries, connections, etc. But those aren't really the issue, it's that once in a blue moon a user will send an unoptimized query, and I'd need to time it

问题 I'm trying to write the most optimal query to find all of the documents that do not have a specific field. Is there any better way to do this than the examples I have listed below? // Get the ids of all documents missing "location" r.db("mydb").table("mytable").filter({location: null},{default: true}).pluck("id") // Get a count of all documents missing "location" r.db("mydb").table("mytable").filter({location: null},{default: true}).count() Right now, these queries take about 300-400ms on a

问题 I have this SQL that works fine. Want the my filter to return the LATEST unique SessionGuids with the highest UserSessionSequenceID. Problem is performance sucks - even though I have good indexes. How can I rewrite this - to omit the ROW_NUMBER line? SELECT TOP(@resultCount) * FROM ( SELECT [UserSessionSequenceID] ,[SessionGuid] ,[IP] ,[Url] ,[UrlTitle] ,[SiteID] ,[BrowserWidth] ,[BrowserHeight] ,[Browser] ,[BrowserVersion] ,[Referer] ,[Timestamp] ,ROW_NUMBER() over (PARTITION BY [SessionGuid

问题 i have this table (500,000 row) CREATE TABLE IF NOT EXISTS `listings` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `type` tinyint(1) NOT NULL DEFAULT '1', `hash` char(32) NOT NULL, `source_id` int(10) unsigned NOT NULL, `link` varchar(255) NOT NULL, `short_link` varchar(255) NOT NULL, `cat_id` mediumint(5) NOT NULL, `title` mediumtext NOT NULL, `description` mediumtext, `content` mediumtext, `images` mediumtext, `videos` mediumtext, `views` int(10) unsigned NOT NULL, `comments` int(11)