add check constraint in mysql code example

Example 1: mysql find db contarint

select *
from information_schema.key_column_usage
where constraint_name='[CONSTRAINT_NAME]'

Example 2: mysql show check constraints

select COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_COLUMN_NAME, REFERENCED_TABLE_NAME
from information_schema.KEY_COLUMN_USAGE
where TABLE_NAME = 'users';