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)...
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...
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...
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 ...
ORDER BY NEWID() UNION是一种在MS SQL Server中使用的操作符,用于合并两个或多个SELECT语句的结果集。它将两个结果集的行组合在一起,并自动去除重复的行。 使用UNION可以将多个查询的结果合并为一个结果集。例如,假设有两个表格,一个存储了学生的英语成绩,另一个存储了学生的数学成绩,可以使用UNION将两个表格...
我们分析下SQL select gf_name,gf_phone from user where user_id=8888 order by gf_name 我们需要按照 gf_name 排序,但是却把 gf_phone 也塞进了 sort_buffer 中 这样 单行数据的大小就等于 gf_name 的长度 + gf_phone 的长度 ,能否让 sort_buffer 中只存 gf_name 字段,这样的话,整体的利用空间就大...
To update data in the database, use the executeUpdate(String SQL) method. This method returns the number of rows matched by the update statement, not the number of rows that were modified. If you do not know ahead of time whether the SQL statement will be a SELECT or an UPDATE/INSERT,...
You need to sort by multiple keys, with each key independently ascending or descending, mimicking the functionality of the SQL ORDER BY clause. Solution Sometimes you get data from a database and need the data ordered in several ways in succession. Rather than doing multiple SELECT queries on...
A PL/SQL Process Order Line (PROCESS_LINE) to update the existing purchase order When a change order request is received, the purchase order information including order quantity and other line item details will be retrieved. Based on user input, a new order quantity will be updated in Oracle...
PL/SQL lets youoverloadsubprogram names and type methods. You can use the same name for several different subprograms as long as their formal parameters differ in number, order, or datatype family. Suppose you want to initialize the firstnrows in two index-by tables that were declared as fol...