[英]How to use count distinct along multiple columns?
输入:
id sem1 sem2 sem3 sem4 sem5 sem6 sem7
1 S O S R null null null
2 O O R R S null null
所需输出:
id O R S
1 1 1 2
2 2 2 1
如果您的数据库支持APPLY/UNPIVOT
符,则使用此
CROSS APPLY
方法
SELECT id,
SUM(CASE WHEN val = 'O' THEN 1 ELSE 0 END) O,
SUM(CASE WHEN val = 'R' THEN 1 ELSE 0 END) R,
SUM(CASE WHEN val = 'S' THEN 1 ELSE 0 END) S
FROM mytable
CROSS apply (VALUES (sem1),
(sem2),
(sem3),
(sem4),
(sem5),
(sem6),
(sem7)) cs(val)
GROUP BY id
UNPIVOT
方法
SELECT id,
SUM(CASE WHEN val = 'O' THEN 1 ELSE 0 END) O,
SUM(CASE WHEN val = 'R' THEN 1 ELSE 0 END) R,
SUM(CASE WHEN val = 'S' THEN 1 ELSE 0 END) S
FROM (SELECT *
FROM mytable) a
UNPIVOT (val
FOR col IN ( sem1,
sem2,
sem3,
sem4,
sem5,
sem6,
sem7 )) upv
GROUP BY id
我个人更喜欢CROSS APPLY
方法而不是UNPIVOT
因为它更具可读性。 明智的表现将是相同的
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