Question

我有一个SQL脚本，该脚本具有查询多个表以搜索值的功能，但是它只能检查下一个表（如果第一个表返回空值）。我正在使用case语句，检查IS NULL THEN等-参见下文。必须有一个更简单的方法来做到这一点？

CASE
    WHEN
        CASE
            WHEN
                CASE    
                    WHEN
                        SELECT accountcode from a238 where reference='xyz'
                    IS NULL THEN
                        SELECT accountcode from a241 where reference='xyz'
                    ELSE
                        SELECT accountcode from a238 where reference='xyz'
                END
            IS NULL THEN
                SELECT accountcode from a240 where reference='xyz'
            ELSE
                CASE    
                    WHEN
                        SELECT accountcode from a238 where reference='xyz'
                    IS NULL THEN
                        SELECT accountcode from a241 where reference='xyz'
                    ELSE
                        SELECT accountcode from a238 where reference='xyz'
                END
        END
    IS NULL THEN
        SELECT accountcode from a239 where reference='xyz'
    ELSE
        CASE
            WHEN
                CASE    
                    WHEN
                        SELECT accountcode from a238 where reference='xyz'
                    IS NULL THEN
                        SELECT accountcode from a241 where reference='xyz'
                    ELSE
                        SELECT accountcode from a238 where reference='xyz'
                END
            IS NULL THEN
                SELECT accountcode from a240 where reference='xyz'
            ELSE
                CASE    
                    WHEN
                        SELECT accountcode from a238 where reference='xyz'
                    IS NULL THEN
                        SELECT accountcode from a241 where reference='xyz'
                    ELSE
                        SELECT accountcode from a238 where reference='xyz'
                END
        END
END

此代码有效，但使用和阅读时有点麻烦。有人也可以指导我吗？

欢呼

Answer 1

如果您需要调试或修改某些内容，那么该查询将非常麻烦。在评论中感谢Parfait对完全外部连接的建议。另外，您可以使用COALESCE()替换所有CASE语句。

使用嵌套和类似的表名，我有可能错过了一些东西，但这就是这个主意。

declare @referenceCode varchar(3) = 'xyz'

select 
    COALESCE(a238.accountcode, a241.accountcode, a240.accountcode, a239.accountcode) as account_code
from a238 
full outer join a241 on a241.reference = @referenceCode
full outer join a240 on a240.reference = @referenceCode
full outer join a239 on a239.reference = @referenceCode
where a238.reference = @referenceCode

检查多个SQL表是否为空值

1 个答案: