Question

我是mysql的新手。

我有一个查询来从不同的表中获取计数，它可以正常工作。但是，现在我想将所有3个查询COUNT分成1个，如SUM（COUNT1，COUNT2，COUNT3）

select COUNT(*) as count1, 0 as count2, 0 as count3 from table1 
UNION ALL 
select 0 as count1, COUNT(*) as count2, 0 as count3 from table2 
UNION ALL 
select 0 as count1, 0 as count2, COUNT(*) as count3 from table3

E.g。 count1 = 10，count2 = 20，count3 = 15

然后，我想得到sum = 45

Answer 1

您可以将SUM()放入子查询中，然后SELECT SUM(count) AS total FROM ( SELECT COUNT(*) AS count FROM table1 UNION ALL SELECT COUNT(*) AS count FROM table2 UNION ALL SELECT COUNT(*) AS count FROM table3 ) AS subquery计数。但是没有必要将它们放在每个联合查询的单独列中。

{{1}}

Answer 2

要从表中获取所有计数的总和，您可以将查询编写为

select 
(select COUNT(*) from table1) +
(select COUNT(*) from table2) +
(select COUNT(*) from table3) as total

按照您的方法，您可以将unioined查询包装为子选择，然后对结果应用总和

SELECT SUM(count1) + SUM(count2) + SUM(count3) total
FROM (
    SELECT COUNT(*) AS count1, 0 AS count2, 0 AS count3 FROM table1 
    UNION ALL 
    SELECT 0 AS count1, COUNT(*) AS count2, 0 AS count3 FROM table2
    UNION ALL 
    SELECT 0 AS count1, 0 AS count2, COUNT(*) AS count3 FROM table3
) t

如何获取所有COUNT的总和？

2 个答案: