Question

我想在SELECT中使用SELECT来获取一些值（我已经完成了这个）问题是，我想在mysql中显示这些数据，总和，这就是问题所在。

我不会发布原始代码，但请查看此示例。

SELECT id, (SELECT COUNT(x) FROM xyz where id=usr.id) as value_1,
(SELECT COUNT(y) FROM zyx where id=usr.id) as value_2 
FROM users AS usr

这是正确的，但我想将value_1和value_2相加。

当我这样做时

SELECT id,
(SELECT COUNT(x) FROM xyz where id=usr.id) as value_1, 
(SELECT COUNT(y) FROM zyx where id=usr.id) as value_2, 
(value_1+value_2) as my_sum_value
FROM users AS usr

我收到有关“value_1”和“value_2”未找到的信息。

我发现，我可以使用

SELECT id, 
(SELECT COUNT(x) FROM xyz where id=usr.id) as value_1, 
(SELECT COUNT(y) FROM zyx where id=usr.id) as value_2, 
((SELECT COUNT(x) FROM xyz where id=usr.id) as value_1, 
(SELECT COUNT(y) FROM zyx where id=usr.id)+
(SELECT COUNT(y) FROM zyx where id=usr.id) as value_2) as my_sum_value
FROM users AS usr

但是，我必须写“两次”我的所有代码。为什么我不能使用名为“value_1”和“value_2”的“别名”？查询后，这个值是否正确，如何访问总和值？

Answer 1

试试这个

SELECT id,
    SUM(
    (SELECT COUNT(x) FROM xyz where id=usr.id), 
    (SELECT COUNT(y) FROM zyx where id=usr.id)
    ) as my_sum_value
FROM users AS usr

你不能使用变量，因为它们在子查询中......

SUM使用子查询

1 个答案: