One: add constraints
1. Add a unique constraint: alter table student add constraint uk_name unique(name);
2. Add foreign key constraints:
alter table table name
add constraint fk_fieldname
foreign key (field name) references associated table name (associated field name)
3. Add check constraint:
alter table table name
add constraint CK_fieldname
check (conditional expression)
4. Add a default value constraint:
alter table table name
add constraint DF_fieldname
default 'default value' for field name
5. Remove constraints:
alter table table name
drop constraint constraint name
Two: query constraints and triggers
1. Query constraints: SELECT * FROM information_schema.`TABLE_CONSTRAINTS`; (you can agree to only query a table by where table_name='student')
In fact, every time a constraint is added, the information of the added constraint is stored in the table_constraints table of the schema information_schema; (The `` in mysql is very similar to that of bash, and the expression in `` is also executed instead of using it as a string. )
2. View all triggers: select* from information_schema.triggers;