Question

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')

Answer 1

Even if MySQL enforced CHECK constraints, I’d still be creating a COURSE_LEVEL table:

• COURSE_LEVEL_CODE, VARCHAR(3), primary key
• COURSE_LEVEL_DESCRIPTION, VARCHAR(120)

…and create a FOREIGN KEY constraint on the COURSE table, clevel column:

ALTER TABLE COURSE
ADD FOREIGN KEY (clevel) REFERENCES COURSE_LEVEL(COURSE_LEVEL_CODE)