[英]Use “result expression” from CASE expression in WHERE clause
是否可以通过使用WHERE
子句中CASE
表达式的结果表达式(weight_class)来过滤SQL Server中的记录? 我无法让它工作,因为我收到一个错误说:
列名称'weight_class'无效
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'
SQL-Server需要一个表别名:
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'
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
) t
WHERE weight_class = 'Cruiserweight'
我想你将不得不使用HAVING
而不是WHERE
:
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
HAVING weight_class = 'Cruiserweight'
编辑:
顺便问一下,你为什么不用它:
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 > 214 AND weight <= 200
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