缩短 SQL 个条件

Question

我有一个 SQL 有一些条件，例如：

SELECT
  CASE WHEN RIGHT(CAST(COLUMN_A as nvarchar(max)),1) = '.' THEN
  SUBSTRING (COLUMN_A, DATALENGTH(COLUMN_A) - 4, 4) ELSE
  SUBSTRING (COLUMN_A, DATALENGTH(COLUMN_A) - 3, 4) END AS COL_1

在同一个 select 中，我让其他人使用上述规则进行检查，我必须全部重复一遍。我正在寻找一种不重复其余代码的方法，有些东西喜欢：

CASE
  WHEN COL_1 LIKE 'AAAA' OR
  COL_1 LIKE 'BBBB' OR
  COL_1 LIKE 'CCCC' OR
  COL_1 LIKE 'DDDD' THEN 1 ELSE 0 END AS Code

使用上述 COL_1 的结果进行其他检查。我怎样才能做到这一点？谢谢

Answer 1

您可以像这样使用嵌套的 SELECT 命令：

SELECT CASE
  WHEN x.COL_1 LIKE 'AAAA' OR
  x.COL_1 LIKE 'BBBB' OR
  x.COL_1 LIKE 'CCCC' OR
  x.COL_1 LIKE 'DDDD' THEN 1 ELSE 0 END AS Code
FROM (
SELECT
  CASE WHEN RIGHT(CAST(COLUMN_A as nvarchar(max)),1) = '.' THEN
  SUBSTRING (COLUMN_A, DATALENGTH(COLUMN_A) - 4, 4) ELSE
  SUBSTRING (COLUMN_A, DATALENGTH(COLUMN_A) - 3, 4) END AS COL_1
) x

Answer 2

SELECT *
FROM   (
        SELECT list_of_columns
             , CASE WHEN this=cool THEN 1 ELSE 0 END As computed_column
        FROM   ...
       ) As a_subquery
WHERE  computed_column = 1

Answer 3

CASE 语法应该是这样的：

CASE
  WHEN COL_1 LIKE 'AAAA' THEN 1 
  WHEN COL_1 LIKE 'BBBB' THEN 1 
  WHEN COL_1 LIKE 'CCCC' THEN 1 
  WHEN COL_1 LIKE 'DDDD' THEN 1 
ELSE 0 
END AS Code

Answer 4

翻转，即在子字符串中执行大小写：

SELECT
  SUBSTRING (COLUMN_A, DATALENGTH(COLUMN_A) -
    CASE WHEN RIGHT(CAST(COLUMN_A as nvarchar(max)),1) = '.' THEN then 4 else 3 end, 4) AS COL_1

并使用 IN 表示不同的值，如果需要验证长度（LIKE 和尾随空格...）

CASE
  WHEN COL_1 IN ('AAAA','BBBB','CCCC','DDDD') and LENGTH(col_1) = 4 THEN 1
  ELSE 0 END AS Code

缩短 SQL 个条件

Shorten SQL conditions

sql

sql-server-2008-r2