mysql casewhen
时间: 2023-09-12 17:11:10 浏览: 59
MySQL中的CASE WHEN语句是一种条件判断语句,它可以根据满足的条件执行不同的操作。当满足某个条件时,该条件下的代码块会被执行,并且后续的条件不再考虑。CASE WHEN语句可以用于SELECT语句中的列值替换、WHERE子句中的条件判断和GROUP BY子句中的分组排序。
例如,以下是一个使用CASE WHEN语句的示例:
SELECT CASE WHEN parent_id < 3 THEN '<3'
WHEN parent_id >= 3 AND parent_id < 5 THEN '>=3 && <5'
ELSE '>=5'
END AS parent_id_new,
count(*) AS num_count,
parent_id,
type_id,
type_name
FROM tdb_goods_types
GROUP BY parent_id_new
ORDER BY num_count;
在上述示例中,根据parent_id的不同取值,使用CASE WHEN语句将parent_id分为三个不同的区间,并将其分组为parent_id_new。然后,统计每个分组中的记录数,并按照记录数进行排序。最终的查询结果包含parent_id_new、num_count、parent_id、type_id和type_name这些列的值。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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