MYSQL 约束 - 多重检查
好吧，我在这里为我正在处理的数据库编写一些约束，我想知道我是否可以执行以下操作：
ALTER TABLE Course
ADD CONSTRAINT cs_level
CHECK (clevel in ('P','I','II','III'))
...而不是这样：
ALTER TABLE Course
ADD CONSTRAINT cs_level
CHECK (clevel = 'P' OR clevel = 'I' OR clevel = 'II' OR clevel = 'III')
Well i am here writing some constraints for a db I am working on and i was wondering if I could do the following:
ALTER TABLE Course
ADD CONSTRAINT cs_level
CHECK (clevel in ('P','I','II','III'))
...instead of this:
ALTER TABLE Course
ADD CONSTRAINT cs_level
CHECK (clevel = 'P' OR clevel = 'I' OR clevel = 'II' OR clevel = 'III')
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即使 MySQL 强制执行
CHECK约束，我仍然会创建一个COURSE_LEVEL表：COURSE_LEVEL_CODE、VARCHAR(3)、主键COURSE_LEVEL_DESCRIPTION、VARCHAR(120)...并在
COURSE表的clevel列上创建 FOREIGN KEY 约束：Even if MySQL enforced
CHECKconstraints, I'd still be creating aCOURSE_LEVELtable:COURSE_LEVEL_CODE, VARCHAR(3), primary keyCOURSE_LEVEL_DESCRIPTION, VARCHAR(120)...and create a FOREIGN KEY constraint on the
COURSEtable,clevelcolumn:不幸的是，MySQL 不支持 CHECK 约束。它们被解析但被忽略。
来自参考手册：
您可以尝试在插入行之前将此检查约束放入业务逻辑中。
正如Joe Celko在他的书中Joe Celko 的 Smarties SQL :
确实有点苛刻，但在某种程度上他是正确的，因为 MySQL 不支持一堆标准SQL 功能。
Unfortunately, MySQL does not support the CHECK-constraints. They are parsed but ignored.
From the reference manual:
You can try to put this check constraint in your business logic before inserting the row.
As Joe Celko says in his book Joe Celko's SQL for Smarties:
A little harsh indeed, but in a way he's correct, since MySQL doesn't support a bunch of Standard SQL features.
MySQL只支持外键约束，不支持检查约束。无论您从哪里获得该语法，都不是 MySQL 手册。
MySQL only supports foreign key constraints, not check constraints. Wherever you got that syntax from, it wasn't the MySQL manual.