一个带有两个where子句的查询中的两个sql总和[重复]答案

【问题标题】：Two sql sums in one query with two where clauses [duplicate]一个带有两个where子句的查询中的两个sql总和[重复]
【发布时间】：2016-04-27 19:51:20
【问题描述】：

您好，我想将两条 sql 语句合并为一条，这样数据将显示在一个查询中。

以下 sql 查询工作正常：

SELECT SUM(CAST(CAST(Amount AS float) AS INT)) AS TotalSponsor
FROM Fees WHERE(Sponsor = 'True')

SELECT SUM(CAST(CAST(Amount AS float) AS INT)) AS TotalLoan
FROM Fees WHERE(StudentLoan = 'True')

基本上我想加入他们，所以输出会是这样的：

TotalSponsor   TotalLoan
10000          5000

任何帮助将不胜感激。

谢谢

【问题讨论】：

标签： mysql select casting sum

【解决方案1】：

您可以将这两行与CROSS JOIN 组合在一起。通常建议不要这样做，因为如果您交叉连接两个表，每个表有 M 行和 N 行，您会在结果中得到 MxN 行（可以是 lot），但在这种情况下，您知道一个事实M 和 N 都是 1，所以 MxN 也是 1。

SELECT *
FROM (
    SELECT SUM(CAST(CAST(Amount AS float) AS INT)) AS TotalSponsor
    FROM Fees WHERE(Sponsor = 'True')
) AS x
CROSS JOIN (
    SELECT SUM(CAST(CAST(Amount AS float) AS INT)) AS TotalLoan
    FROM Fees WHERE(StudentLoan = 'True')
) AS y

【讨论】：

【解决方案2】：

一个选项，条件聚合......

SELECT SUM(IF(f.Sponsor    ='True',CAST(CAST(Amount AS float) AS INT),0)) AS TotalSponsor
     , SUM(IF(f.StudentLoan='True',CAST(CAST(Amount AS float) AS INT),0)) AS TotalLoan
  FROM Fees f
 WHERE f.Sponsor = 'True'
    OR f.StudentLoan = 'True'

IF() 函数将第一个参数计算为布尔值，如果计算结果为 TRUE，则返回第二个参数，否则返回第三个参数。

您可以使用 CASE 表达式代替 IF 来实现等效行为...

 SUM(CASE WHEN  somecondition  THEN  somevalue  ELSE 0 END)

或者，您可以在外部查询的 SELECT 列表中使用 sbqueries，如下所示：

SELECT ( SELECT SUM(CAST(CAST(Amount AS float) AS INT))
           FROM Fees
          WHERE(Sponsor = 'True') 
       ) AS TotalSponsor
     , ( SELECT SUM(CAST(CAST(Amount AS float) AS INT))
           FROM Fees
           WHERE(StudentLoan = 'True')
       ) AS TotalLoan

或者，您可以将查询用作内联视图

SELECT s.TotalSponsor
     , l.TotalLoan
  FROM ( SELECT SUM(CAST(CAST(Amount AS float) AS INT)) AS TotalSponsor
           FROM Fees WHERE(Sponsor = 'True') 
       ) s
 CROSS
  JOIN  ( SELECT SUM(CAST(CAST(Amount AS float) AS INT)) AS TotalLoan
            FROM Fees WHERE(StudentLoan = 'True')
       ) l

【讨论】：