[英]SELECT inside a COUNT
我想在COUNT中嵌入一个SELECT,但我找不到任何例子。
#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
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
您可以在子选择内移动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
使用SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d
。
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
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