替代在 ON 子句中使用 IIF 以提高可读性

Question

我的同事发现 IIF 在以下上下文中的用法很难理解。

是否有更易读的替代方法？

DROP TABLE IF EXISTS #Cas;
CREATE TABLE #Cas( OP VARCHAR(10), BR  VARCHAR(10), SCORE INT)
INSERT INTO #Cas
    values
        ('A','X', 10),
        ('A','Y', 5),
        ('B','J', 6),
        ('C','Q', 50)

DROP TABLE IF EXISTS #Target;
CREATE TABLE #Target( OP VARCHAR(10), BR  VARCHAR(10) )
INSERT INTO #Target
    values
        ('A','ALL')

SELECT  C.OP,
        SUM(C.SCORE)
FROM    #Cas C
        INNER JOIN #Target T
            ON 
            C.OP = T.OP AND
            C.BR = IIF(T.BR = 'ALL', C.BR, T.BR)
GROUP BY C.OP

Answer 1

您可以只使用逻辑 or 运算符，或者更好 - in 运算符来简化它：

SELECT  C.OP,
        SUM(C.SCORE)
FROM    #Cas C
        INNER JOIN #Target T
            ON 
            C.OP = T.OP AND
            T.BR IN (C.BR, 'ALL')
GROUP BY C.OP

Answer 2

可以用OR来明确t.br等于ALL或者等于c.br:

AND (t.br = 'ALL' or c.br = t.br)

或更简洁：

AND t.br in ('ALL', c.br)

Answer 3

IIF 是 CASE 的语法糖。你可以这样写你的 on 子句：

ON 
C.OP = T.OP AND
C.BR = CASE WHEN T.BR = 'ALL' THEN C.BR ELSE T.BR END

Answer 4

我一般用NULL来标识具体情况(f.e."all")。因此，代码可能如下所示：

CREATE TABLE #Cas( OP VARCHAR(10), BR  VARCHAR(10), SCORE INT)
INSERT INTO #Cas
    values
        ('A','X', 10),
        ('A','Y', 5),
        ('B','J', 6),
        ('C','Q', 50)


CREATE TABLE #Target( OP VARCHAR(10), BR  VARCHAR(10) )
INSERT INTO #Target
    values
        ('A', NULL)

SELECT  C.OP,
        SUM(C.SCORE)
FROM    #Cas C
        INNER JOIN #Target T
            ON 
            C.OP = T.OP AND
            C.BR = ISNULL(T.BR, C.BR)
GROUP BY C.OP

替代在 ON 子句中使用 IIF 以提高可读性

Alternative to using IIF in ON clause to increase readability

sql

sql-server

select

iif