Question

我正在努力使这个查询工作，但我无法理解我做错了什么。我看到了同样问题的其他问题，但我还是不明白。

SELECT DoctorsVisits.VisitDate,
       (SELECT COUNT(1) AS Total
        FROM DoctorsVisits
        WHERE (DoctorsVisits.PeriodOfVisitId=2)
        GROUP BY DoctorsVisits.VisitDate) AS Manhas
FROM DoctorsVisits;

Answer 1

你确定你不是只想要一个没有子查询的普通组吗？

SELECT DoctorsVisits.VisitDate, count(*) as Manhas
FROM DoctorsVisits
group by DoctorsVisits.VisitDate

或者也许：

SELECT DoctorsVisits.VisitDate,
       sum(case when DoctorsVisits.PeriodOfVisitId=2 then 1 else 0 end) as Manhas
FROM DoctorsVisits
group by DoctorsVisits.VisitDate

Answer 2

您可以执行以下操作。您为COUNT使用了不必要的子查询。

SELECT  DoctorsVisits.VisitDate, COUNT(*) As Total 
FROM    DoctorsVisits
WHERE   DoctorsVisits.PeriodOfVisitId=2
GROUP BY DoctorsVisits.VisitDate

子查询返回的值超过1 - 错误

2 个答案: