Although , When we have designed our database he/she knows what type of constraints is require to make data perfect and the Database designer applies those constraints but it might be possible that sometime we have to disable those constraints make some tweak with the data in the table and then again enable the constraints.
Below are two simple command to Enable & Disable constraints of a table.
a) Disable constraints on a table
ALTER TABLE tableName NOCHECK CONSTRAINT ALL
b) Enable Constraints on a table
ALTER TABLE TABLE_NAME CHECK CONSTRAINT ALL
Lets understand this by an example suppose, I have city_seed table which having Foreign key constraint of country_seed table.
Now when we run disable constraint command as shown above then you will find the constraint is disable as shown in figure
Now when we run enable constraint then see below figure
I hope it might helpful you somewhere.
Thanks & Enjoy!!!