Optimizing a self join queryPosted by: Dan Cummings Date: January 03, 2007 03:50PM I have a query which requires that I get the minumum date in a group then retrieve data from that record that has the minimum date. I read an article that suggested avoiding self joins by using ...
UPDATE JOIN是MySQL中一种结合UPDATE语句和JOIN操作的技术,用于根据一张表或多张表的数据来更新另一张表的数据。它可以根据指定的连接条件将两个或多个表连接起来,并根据连接的结果更新目标表中的数据。 UPDATE JOIN的语法 下面是UPDATE JOIN的基本语法: UPDATE目标表 JOIN表1ON连接条件1 [JOIN表2ON连接条件2] ....
Execute the self join shown and observe that b.stop gives all the places you can get to from Craiglockhart, without changing routes. Change the query so that it shows the services from Craiglockhart to London Road. */ SELECT a.company, a.num, a.stop, b.stop FROM route a JOIN route ...
MySQL更新查询优化-子查询? 、、 哪个查询将是最快的:我自己的测试没有显示任何明显的结果:UPDATE items, brands SET items.brand_id = brands.id WHERE brands.name= 'apple'query2:我在Google上找不到任何关于这方面的数据;也许这里的一些SQL专家知道答案?
You use the self join when you want to combine rows with other rows in the same table. To perform the self join operation, you must use a table alias to help MySQL distinguish the left table from the right table of the same table in a single query. MySQL self join examples# Let’s...
select id, name from stops join route on stops.id=route.stop where num=4 and company='LRT'; The query shown gives the number of routes that visit either London Road (149) or Craiglockhart (53). Run the query and notice the two services that link these stops have a count of 2. Add...
题目链接 Self join - SQLZOO 截图记录下sqlzoo.net上的答题情况。 第十个问题比较复杂,答案参考以下链接: sqlzoo练习答案--Self join 代码如下: SELECT DISTINCT bus1.num, bus1.company, name, bus2.num, bus2.company FROM ( SELECT start1.num, start1.company, stop1.stop FROM route AS start1 JO...
(*)` from `test`.`testi` `t1` join `test`.`testi` `t2` where (`test`.`t2`.`c1` between `test`.`t1`.`c1` and (`test`.`t1`.`c1` + 30)) group by `test`.`t1`.`id` 1 row in set (0.00 sec) mysql> alter table testi engine=InnoDB; Query OK, 65536 rows affected ...
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I used to do SQL query many years ago, but have gone rusty in recent years. I need help on this query, and I am hoping good Samaritans here will help me out. Good thing is all the data is available in 1 table. So the table has many columns, but only 4 are important. ...