如何在MySQL中正确使用CASE..WHEN [英] How do I use properly CASE..WHEN in MySQL
本文介绍了如何在MySQL中正确使用CASE..WHEN的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
这是一个演示查询,请注意,它非常简单,仅在base_price为0的情况下提取, 仍然选择条件3:
Here is a demo query, notice it is very simple, Fetches only where base_price is 0, And still, it chooses the condition 3:
SELECT
CASE course_enrollment_settings.base_price
WHEN course_enrollment_settings.base_price = 0 THEN 1
WHEN course_enrollment_settings.base_price<101 THEN 2
WHEN course_enrollment_settings.base_price>100 AND
course_enrollment_settings.base_price<201 THEN 3
ELSE 6
END AS 'calc_base_price',
course_enrollment_settings.base_price
FROM
course_enrollment_settings
WHERE course_enrollment_settings.base_price = 0
base_price
是decimal(8,0)
在我的数据库上运行它时,我得到:
When run this on my DB, I get:
3 0
3 0
3 0
3 0
3 0
3 0
3 0
3 0
3 0
3 0
推荐答案
在CASE
之后立即删除course_enrollment_settings.base_price
:
SELECT
CASE
WHEN course_enrollment_settings.base_price = 0 THEN 1
...
END
CASE
具有两种不同的形式,如手册中所述.在这里,由于要使用搜索条件
CASE
has two different forms, as detailed in the manual. Here, you want the second form since you're using search conditions.
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