嵌入在 sum() 函数中的 T-SQL IF 语句

问题描述

我正在尝试将 MySQL 查询转换为 T-SQL 查询，而 SUM 语句中包含的 IF 语句让我感到困惑.有什么建议吗?

I'm attempting to convert a MySQL query to a T-SQL query and the IF statement that's enclosed within a SUM statement is tripping me up. Any suggestions?

SELECT
    CMTS_RQ.[Dated],
    CMTS_RQ.CMTS_Name,
    Count(CMTS_RQ.CMTS_Name) AS emat_count,
    Sum(if(CMTS_RQ.US_Pwr>=37 and CMTS_RQ.US_Pwr<=49)) AS us_pwr_good
FROM
    CMTS_RQ
GROUP BY
    CMTS_RQ.CMTS_Name,
    CMTS_RQ.[Dated]

但我收到一个错误:

消息 156，级别 15，状态 1，第 5 行
关键字if"附近的语法不正确.
消息 102，级别 15，状态 1，第 5 行
')' 附近的语法不正确.

Msg 156, Level 15, State 1, Line 5
Incorrect syntax near the keyword 'if'.
Msg 102, Level 15, State 1, Line 5
Incorrect syntax near ')'.

推荐答案

T-SQL 没有内联"IF 语句 - 使用 CASE 代替:

T-SQL doesn't have a "inline" IF statement - use a CASE instead:

SELECT
    CMTS_RQ.[Dated],
    CMTS_RQ.CMTS_Name,
    Count(CMTS_RQ.CMTS_Name) AS emat_count,
    Sum(CASE 
           WHEN CMTS_RQ.US_Pwr >=37 AND CMTS_RQ.US_Pwr <= 49 
             THEN 1
             ELSE 0 
        END) AS us_pwr_good
FROM
    CMTS_RQ
GROUP BY
    CMTS_RQ.CMTS_Name,
    CMTS_RQ.[Dated]

因此，如果 CMTS_RQ.US_Pwr 的值是 >= 37 AND <= 49 然后将 SUM 加 1 - 否则0. 这是否为您提供了您想要的东西?

So if the value of CMTS_RQ.US_Pwr is >= 37 AND <= 49 then add 1 to the SUM - otherwise 0. Does that give you what you're looking for?

在 SQL Server 2012 和更新版本中，您可以使用新的 IIF 函数:

In SQL Server 2012 and newer, you can use the new IIF function:

SUM(IIF(CMTS_RQ.US_Pwr >= 37 AND CMTS_RQ.US_Pwr <= 49, 1, 0)) AS us_pwr_good

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