在mysql中除以计数结果

Question

SELECT COUNT(*) FROM Table1 WHERE user = "carl" AND ans = "yes"

然后我想将此查询的输出除以另一个查询，例如输出为10.所以它将如下：

10 / SELECT COUNT(*) From Table1 WHERE user = "carl"

如何正确的语法？

谢谢

Answer 1

您想要使用条件聚合和除法。您不需要两个查询：

SELECT SUM(ans = 'yes')/COUNT(*)
FROM Table1
WHERE user = 'carl';

SUM(ans = 'yes')计算yes的行数。实际上，您可以进一步简化为：

SELECT avg(ans = 'yes')
FROM Table1
WHERE user = 'carl';

Answer 2

您可以通过将两个查询作为子查询运行来执行此操作：

SELECT 
  (SELECT COUNT(*) FROM Table1 WHERE user = "carl" AND ans = "yes") / 
  (SELECT COUNT(*) From Table1 WHERE user = "carl")

Answer 3

做一个

SELECT (10/COUNT(*)) AS `myVariable` FROM `Table1` WHERE...

然后根据需要使用myVariable。