基于Age SQL的计数

Question

我有以下T-SQL来计算年龄：

SELECT
  Member_ID,
  DATEDIFF(YY,DOB,GETDATE()) - 
  CASE 
    WHEN DATEADD(YY,DATEDIFF(YY,DOB,GETDATE()),DOB) > GETDATE() THEN 1
    ELSE 0
  END AS Age in Years
FROM MEMBER
WHERE YEAR(registration_date ) >= 2012

如何计算每个年龄段的会员ID数量？

Answer 1

我会使用子查询或CTE来完成此操作。更容易理解：

SELECT AgeInYears, COUNT(*)
FROM (SELECT Member_ID,
             (DATEDIFF(YY,DOB,GETDATE()) - 
              CASE WHEN DATEADD(YY,DATEDIFF(YY,DOB,GETDATE()),DOB) > GETDATE() THEN 1
                   ELSE 0
              END) AS AgeinYears
      FROM MEMBER
      WHERE YEAR(registration_date ) >= 2012
     ) m
GROUP BY AgeInYears
ORDER BY 1;

Answer 2

这样的事情：

SELECT
-- Member_ID,  commented out
DATEDIFF(YY,DOB,GETDATE()) - 
CASE 
WHEN DATEADD(YY,DATEDIFF(YY,DOB,GETDATE()),DOB) > GETDATE() THEN 1
ELSE 0
END AS Age in Years
, count(member_id) membersWithThisAge
FROM MEMBER
WHERE YEAR(registration_date ) >= 2012
group by DATEDIFF(YY,DOB,GETDATE()) - 
CASE 
WHEN DATEADD(YY,DATEDIFF(YY,DOB,GETDATE()),DOB) > GETDATE() THEN 1
ELSE 0
END

member_id不能包含在select子句中。如果是，那么你会得到每个成员一个年龄的计数。