MYSQL 中的 SUM（子查询）
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时间：2020-08-31 22:16:41 来源:igfitidea点击:
SUM(subquery) in MYSQL
提问by D?nu
Basically, I am trying the following:
基本上，我正在尝试以下操作：
SELECT m.col1, SUM(SELECT col5 FROM table WHERE col2 = m.col1)
FROM table AS m
This doesn't seem to work. Is there any solution?
这似乎不起作用。有什么解决办法吗？
回答by Mithrandir
Why don't you do this:
你为什么不这样做：
SELECT m.col1, (SELECT SUM(col5) FROM table WHERE col2 = m.col1)
FROM table AS m
回答by SergeS
yes - use joins
是 - 使用连接
SELECT m.col1, SUM(j.col5) FROM table AS m
JOIN table AS j ON j.col2 = m.col1 GROUP BY m.col1
回答by Rolice
Sum is used inside the second select, where we want to sum the column. The col2 may be ambiguous column, if such column exists in the table m.
Sum 用于第二个选择中，我们要在其中对列求和。如果表 m 中存在这样的列，则 col2 可能是不明确的列。
SELECT
m.col1,
(SELECT SUM(t.col5) FROM table AS t WHERE t.col2 = m.col1) AS sumcol
FROM table AS m
