Check out example codes for "mysql find db contarint". It will help you in understanding the concepts better.

Code Example 1

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

Code Example 2

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

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