在COUNT裏面選擇

我想在COUNT裏面嵌入一個SELECT，但是我找不到任何例子。在COUNT裏面選擇

#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

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2010-07-16 Issac Kelly

你並不真的需要一個子選擇：

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

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2010-07-16 16:35:04

+1這更有效地解決了OP的特定查詢。因爲只有2個狀態，所以我會使用'IF（）'而不是'CASE'，但刪除子查詢是正確的。 – 2010-07-16 17:23:11

您可以將內部的計數（）的子選擇：

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

來源

2010-07-16 16:29:04

所以，選擇一個數裏面是SQL語法錯誤？ – Ahmad 2016-10-19 15:37:31

@Ahmad，這是正確的，至少對於MySQL來說。 – 2016-10-21 21:32:18

使用SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const') as d。

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2010-07-16 16:29:07 Femaref

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

來源

2010-07-16 16:29:52 Jeroen

在COUNT裏面選擇

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