5.执行select count(1) from order o where o.user_id in (select u.id where users); 因为我们开启了慢查询,且设置了超过1秒钟的就为慢查询,此sql执行了24秒,所以属于慢查询。 我们在日志中查看: more /var/lib/mysql/localhost-slow.log, 我们可以看到查询的时间,用户,花费的时间,使用的数据库,执行的...
select country_code, country_name, capital from countries order by capital; Powered By The results would be - That is it for this tutorial. In this tutorial, you learned to use the order by keyword in SQL to sort column values. If you want to strengthen your SQL knowledge, you chec...
5.执行select count(1) from order o where o.user_id in (select u.id where users); 因为我们开启了慢查询,且设置了超过1秒钟的就为慢查询,此sql执行了24秒,所以属于慢查询。 我们在日志中查看: more /var/lib/mysql/localhost-slow.log, 我们可以看到查询的时间,用户,花费的时间,使用的数据库,执行的...
1.利用子查询进行过滤 例子:当前有三个表 orders,orderitems,customers orders:订单号(主键)、订单日期、订单客户ID(关联customers的cust_id) orderitems:订单编号(主键),订单物品号(主键) customers:客户ID(主键) 问题:需要列出订购物品TNT2(prod_id)的所有客户名称(cust_name,cust_contanct),需要怎样检索? (1)...
CREATEDEFINER=`root`@`%`PROCEDURE`test_insertdata`(IN`loopcount`INT) LANGUAGE SQLNOTDETERMINISTICCONTAINSSQL SQL SECURITY DEFINER COMMENT''BEGINdeclarev_uuidvarchar(50);whileloopcount>0dosetv_uuid=uuid();insertintotest_order (user_id,order_id,order_status,create_date)values(rand()*1000,id,rand...
1. Sorting by column in ascending order Here we use ORDER BY to sort the “hiredate” column in asc (ascending) order: postgres=#selectempno,ename,hiredatefromemporderbyhiredateasc;empno | ename | hiredate---+---+---7369 | SMITH | 1980-12-17 00:00:00 7499 | ALLEN | 19...
通过explain查看sql的执行计划时,Extra字段的值往往会看到Using where; Using index; Using temporary; Using filesort 一、using filesort 在使用order by关键字的时候,如果待排序的内容不能由所使用的索引直接完成排序的话,那么mysql有可能就要进行文件排序。
With theCOLLATEclause, you can override whatever the default collation is for a comparison.COLLATEmay be used in various parts of SQL statements. Here are some examples: WithORDER BY: SELECTkFROMt1ORDERBYkCOLLATElatin1_german2_ci; WithAS: ...
接口定位:无复杂逻辑,定位到具体SQL SQL分析: image.png 无索引命中,a表全表扫描 Extra Using filesort Using filesort 是什么意思? 官方的定义是,MySQLmust do an extra pass to find out how to retrieve the rows in sorted order. The sort is done by going through all rows according to the join ...
优化mysql使用order by导致执行效率低,出现Using temporary; Using filesort 1、Sql语句 2、去掉ORDER BY,效率提升 3、 给ORDER BY 加上索引,问题没有解决 上面的sql语句中,别名为a的表使用了两个字段,一个是外键PRODUCTONESORTVMID,一个是排序PUBLISH_DATE 两个字段分别加索引。查询结果,效率没有任何提升。 4...