MySQL中多个表的COUNT(*)

您可以通过使用子查询来完成,每个tableCount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

您可以使用子查询来执行此操作,例如:

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

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

这里有一种简单的方法,可以从多个表中获得行计数(如果有) 特定表上没有条件

注:

对于InnoDB,此计数是 近似值 . 然而,对米桑来说,这个数字是准确的。

引自 docs :

行数。一些存储引擎(如MyISAM)存储 精确计数。对于其他存储引擎,如InnoDB,此值为 到50%。在这种情况下,请使用SELECT COUNT(*)获得准确的计数 数一数。

information_schema.tables

SELECT 
    table_name, 
    table_rows
FROM 
    information_schema.tables
WHERE
    table_name like 'my_table%';

输出:

table_name    table_rows
my_table_1    0
my_table_2    15
my_table_3    30

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