错误选择内部计数

Question

我有这个程序

SELECT COUNT( a.id_badania ) AS iloscBadan, COUNT( b.zdjecie ) AS iloscZdjec, COUNT (SELECT id_badania FROM Badania WHERE status='W trakcie realizacji';)
FROM Badania a
INNER JOIN Zdjecia b ON a.id_badania = b.id_badania

而这个错误

您的SQL语法有误； 在第1行的“ SELECT id_badania FROM Badania WHERE status ='W trakcie realizacji'）FROM Badani”中检查与您的MySQL服务器版本相对应的手册以使用正确的语法

我不太了解sql。

Answer 1

您可以使用带有case语句的sum来计算特定状态的值

    SELECT COUNT( a.id_badania )   AS iloscBadan, COUNT( b.zdjecie ) AS iloscZdjec, Sum( case when status='W trakcie realizacji' then 1 else 0 end ) 
     FROM Badania a
     INNER JOIN Zdjecia b ON a.id_badania = b.id_badania

Answer 2

您不能将子查询放在聚合函数中。 并且在查询中间有一个分号。 我猜想您只需要条件聚合。 可以这样：

SELECT COUNT( a.id_badania ) AS iloscBadan, COUNT( b.zdjecie ) AS iloscZdjec,
       SUM(status = 'W trakcie realizacji')
FROM Badania a INNER JOIN
     Zdjecia b
     ON a.id_badania = b.id_badania;

要么：

SELECT COUNT( a.id_badania ) AS iloscBadan, COUNT( b.zdjecie ) AS iloscZdjec,
       COUNT(DISTINCT case when status = 'W trakcie realizacji' then a.id_badania end)
FROM Badania a INNER JOIN
     Zdjecia b
     ON a.id_badania = b.id_badania;