来自MySQL中多个表的COUNT（*）

How do I go about selecting COUNT(*)s from multiple tables in MySQL?

如何从MySQL中的多个表中选择COUNT（*）？

Such as:

如：

SELECT COUNT(*) AS table1Count FROM table1 WHERE someCondition
JOIN?? 
SELECT COUNT(*) AS table2Count FROM table2 WHERE someCondition
CROSS JOIN? subqueries?
SELECT COUNT(*) AS table3Count FROM table3 WHERE someCondition

Edit:

编辑：

The goal is to return this:

目标是返回：

+-------------+-------------+-------------+
| table1Count | table2Count | table3Count |
+-------------+-------------+-------------+
| 14          | 27          | 0           |
+-------------+-------------+-------------+

4 个解决方案

#1

You can do it by using subqueries, one subquery for each tableCount :

您可以使用子查询来执行此操作，每个tableCount都有一个子查询：

SELECT
  (SELECT COUNT(*) FROM table1 WHERE someCondition) as table1Count, 
  (SELECT COUNT(*) FROM table2 WHERE someCondition) as table2Count,
  (SELECT COUNT(*) FROM table3 WHERE someCondition) as table3Count

#2

You can do this with subqueries, e.g.:

您可以使用子查询执行此操作，例如：

select (SELECT COUNT(*) FROM table1 WHERE someCondition) as table1Count, 
       (SELECT COUNT(*) FROM table2 WHERE someCondition) as table2Count

#3

You can use UNION

你可以使用UNION

  SELECT COUNT(*) FROM table1 WHERE someCondition
  UNION
  SELECT COUNT(*) FROM table2 WHERE someCondition
  UNION
  SELECT COUNT(*) FROM table3 WHERE someCondition

#4

Try changing to:

尝试更改为：

SELECT 
    COUNT(table1.*) as t1,
    COUNT(table2.*) as t2,
    COUNT(table3.*) as t3 
FROM table1 
    LEFT JOIN tabel2 ON condition
    LEFT JOIN tabel3 ON condition

#1