使用 MYSQL 在一个查询中选择两个表中的 COUNT

本文介绍了使用 MYSQL 在一个查询中选择两个表中的 COUNT的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

有没有一种方法可以通过一个查询选择带有两个表的 COUNT.

Is there a way i can select the COUNT with two table with one single query.

目前我有以下内容，但无法正常工作.

At the moment i have the following and it doesn't work correctly.

SELECT COUNT(t1.id) as t1_amount, COUNT(t2.id) as t2_amount FROM table1 t1, table2 t2

推荐答案

这是一种方法:

select (select count(*) from table1) as t1_amount, (select count(*) from table2) as t2_amount

这是另一种方式:

select t1.t1_amount, t2.t2_amount from (select count(*) as t1_amount from table1) t1 cross join (select count(*) as t2_amount from table2) t2

您的方法不起作用，因为 from 子句中的 , 执行了 cross join.这会在两个表之间进行笛卡尔积.

Your method does not work because the , in the from clause does a cross join. This does a cartesian product between the two tables.