使用“结果表达式"从WHERE子句中的CASE表达式 [英] Use "result expression" from CASE expression in WHERE clause

问题描述

是否可以通过使用WHERE子句中的CASE表达式的结果表达式(weight_class)来过滤SQL Server中的记录?我无法使它正常工作，因为出现错误消息:

Is it possible to filter records in SQL Server by using a result expression (weight_class) from a CASE expression in the WHERE clause? I can't get it to work because I get an error saying:

无效的列名"weight_class"

Invalid column name 'weight_class'

代码:

SELECT 
    first_name, last_name, 
    weight_class = CASE
                      WHEN weight < 172 THEN 'Welterweight'
                      WHEN weight <= 192 THEN 'Middleweight'
                      WHEN weight <= 214 THEN 'Light heavyweight'
                      WHEN weight <= 220 THEN 'Cruiserweight'
                      ELSE 'Heavyweight'
                   END
FROM 
    athletes

这就是我想要做的:

SELECT 
    first_name, last_name, 
    weight_class = CASE
                      WHEN weight < 172 THEN 'Welterweight'
                      WHEN weight <= 192 THEN 'Middleweight'
                      WHEN weight <= 214 THEN 'Light heavyweight'
                      WHEN weight <= 220 THEN 'Cruiserweight'
                      ELSE 'Heavyweight'
                   END
FROM 
    athletes
WHERE 
    weight_class = 'Cruiserweight'

推荐答案

SQL Server需要表别名:

SQL-Server requires a table alias:

SELECT * from
 (
 SELECT first_name, last_name, 
        CASE
 WHEN weight<172 THEN 'Welterweight'
 WHEN weight<=192 THEN 'Middleweight'
 WHEN weight<=214 THEN 'Light heavyweight'
 WHEN weight<=220 THEN 'Cruiserweight'
  ELSE 'Heavyweight'
  END AS weight_class 
  FROM athletes
 ) as t
 WHERE weight_class = 'Cruiserweight'

这篇关于使用“结果表达式"从WHERE子句中的CASE表达式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！