MySQL 在 COUNT 中选择
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时间：2020-08-31 16:34:10 来源:igfitidea点击:
SELECT inside a COUNT
提问by Issac Kelly
I would like to embed a SELECT inside a COUNT, but I can't find any examples.
我想在 COUNT 中嵌入 SELECT，但找不到任何示例。
#pseudosql
SELECT a AS current_a, COUNT(*) AS b,
COUNT( SELECT FROM t WHERE a = current_a AND c = 'const' ) as d,
from t group by a order by b desc
回答by Justin K
You don't really need a sub-select:
你真的不需要一个子选择：
SELECT a, COUNT(*) AS b,
SUM( CASE WHEN c = 'const' THEN 1 ELSE 0 END ) as d,
from t group by a order by b desc
回答by Ike Walker
You can move the count() inside your sub-select:
您可以在子选择中移动 count() ：
SELECT a AS current_a, COUNT(*) AS b,
( SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d,
from t group by a order by b desc
回答by Femaref
Use SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d.
使用SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d.
回答by Jeroen
SELECT a AS current_a, COUNT(*) AS b,
(SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d
from t group by a order by b desc
