mysql - 如何在一个查询中执行两次 COUNT(*) 获取？

Question

我有一个 MySQL 表

id | string
------------------------------
 1 | one, two, three
 2 | two, three, five
 3 | one, three, four
 4 | three, five
 5 | one, two, three
 6 | two, three, five
 7 | one, three, four
 8 | one, three, five
 9 | two, three, four, five
10 | one, two, three, five

我想获取string列中包含子字符串two的元素的比例。我可以轻松执行两个查询并手动划分它们:

SELECT COUNT(*) FROM `table` WHERE `string` LIKE '%three%'

然后除以

SELECT COUNT(*) FROM `table`

但是我怎样才能只用一个查询来执行此操作呢？

Answer 1

您可以使用 SUM 与 IF 来在括号内给出 1 或 0:-

SELECT SUM(IF(`string` LIKE '%three%', 1, 0))/COUNT(*)  
FROM `table`