Question

table account:
    acID (pri, uni, a-i)
    ...

table patient:
    paID (pri, uni, a-i)
    paAccountID (int, foreign key)
    ...

table test:
    tsID (pri, uni, a-i)
    tsAccountID (int, foreign key)
    tsPatientID (int, foreign key)
    tsStatus (int, ranges 0 to 3)
    tsFlag (int, ranges 0 to 1)

为每位患者检索patient的数据和tsID的数量：

SELECT patient.*, Count(tsID) as tsCount   
FROM account 
LEFT JOIN patient ON acID = paAccountID
LEFT JOIN test ON paID = tsPatientID
WHERE paAccountID=1
GROUP BY paID

现在，我想检索tsFlag=1的数量，tsStatus=0的数量，'tsStatus = 1'的数量...... tsStatus=3的数量。

感谢Explosion Pill的回答：

SELECT patient.*, Count(tsID), SUM(tsStatus=0), 
SUM(tsStatus=1), SUM(tsStatus=2), SUM(tsStatus=3), SUM(tsFlag=1)
FROM account 
LEFT JOIN patient ON acID = paAccountID
LEFT JOIN test ON paID = tsPatientID
WHERE paAccountID=1
GROUP BY paID

像魅力一样工作，但如果NULL为SUM提供Count=0 - 我怎样才能获得0？

Answer 1

您可以使用SUM：

获取X = Y的计数

SELECT patient.*, SUM(tsStatus = 1) AS tsStatus1
FROM ...

您也可以为其他列执行此操作。

您可以使用IFNULL或COALESCE指定默认的非空值：

IFNULL(SUM(tsStatus = 3), 0);

用于检索多个Counts的SQL语句

1 个答案: