带有 CASE 语句的 SQL BETWEEN

Question

我在使案例陈述起作用时遇到了一些困难。我需要在具有许多不同字符和条件的字段上运行 case 语句。我首先需要剥离所有非数字值的字段，然后根据字段的值设置一个值，我已经能够编写一个 case 语句来执行此操作，但是它非常慢。这有效：

CASE
WHEN (SELECT CAST(CAST((SELECT SUBSTRING(fieldtoreplace, Number, 1) FROM master..spt_values WHERE Type='p' AND Number <= LEN(fieldtoreplace) AND SUBSTRING(fieldtoreplace, Number, 1) LIKE '[0-9]' FOR XML Path('')) AS xml) AS varchar(255))) BETWEEN 1 and 10 THEN 'MIN'
WHEN (SELECT CAST(CAST((SELECT SUBSTRING(fieldtoreplace, Number, 1) FROM master..spt_values WHERE Type='p' AND Number <= LEN(fieldtoreplace) AND SUBSTRING(fieldtoreplace, Number, 1) LIKE '[0-9]' FOR XML Path('')) AS xml) AS varchar(255))) BETWEEN 11 and 25 THEN 'MID'
WHEN (SELECT CAST(CAST((SELECT SUBSTRING(fieldtoreplace, Number, 1) FROM master..spt_values WHERE Type='p' AND Number <= LEN(fieldtoreplace) AND SUBSTRING(fieldtoreplace, Number, 1) LIKE '[0-9]' FOR XML Path('')) AS xml) AS varchar(255))) = 26 THEN 'MAX'
ELSE 'UNKNOWN'
END

但是，我希望能够做一些更像下面这样的事情，它只运行一次转换，而不是对 case 语句的每一行。

CASE (SELECT CAST(CAST((SELECT SUBSTRING(fieldtoreplace, Number, 1) FROM master..spt_values WHERE Type='p' AND Number <= LEN(fieldtoreplace) AND SUBSTRING(fieldtoreplace, Number, 1) LIKE '[0-9]' FOR XML Path('')) AS xml) AS varchar(255)))
WHEN BETWEEN 1 and 10 THEN 'MIN'
WHEN BETWEEN 11 and 25 THEN 'MID'
WHEN 26 THEN 'MAX'
ELSE 'UNKNOWN'
END

实际的语句是 41 种不同的 case，有各种 between 和 equals 语句。

有没有人为此提供解决方案，以便只运行一次转换？它运行的表非常大。

两者的输出应该是：

9    MIN
5    MIN
26   MAX
26   MAX
25   MID
44   UNKNOWN

Answer 1

在 SQL Server 中，如果您不想多次运行某些内容，请使用 APPLY：

select . . .,
       (case when v.val between 1 and 10 then 'MIN'
             when v.val between 11 and 25 then 'MID'
             when v.val = 26 then 'MAX'
             else 'UNKNOWN'
        end    
from . . . CROSS APPLY
     (VALUES ( (SELECT CAST(CAST((SELECT SUBSTRING(fieldtoreplace, Number, 1) FROM master..spt_values WHERE Type='p' AND Number <= LEN(fieldtoreplace) AND SUBSTRING(fieldtoreplace, Number, 1) LIKE '[0-9]' FOR XML Path('')) AS xml) AS varchar(255)))
     ) v(val)