MySQL - How to check if exist foreign key

In MySQL, the "IF EXIST" clause doesn't function when checking a foreign key. There is only one method I know to perform this check.

Information regarding constraints is stored in the general MySQL table  "information_schema.TABLE_CONSTRAINTS". 

The "TABLE_NAME" column indicates the table where the constraint exists.
The "CONSTRAINT_NAME" column represents the name of your constraint.
The "CONSTRAINT_TYPE" column defines the type of your constraint; in our case, it is a "FOREIGN KEY".

So, for example, if you want to check all foreign keys in your table:

SELECT *
FROM information_schema.TABLE_CONSTRAINTS 
WHERE TABLE_NAME='name_of_your_table' AND CONSTRAINT_TYPE='FOREIGN KEY';

In my case it shows:

CONSTRAINT_CATALOG	CONSTRAINT_SCHEMA	CONSTRAINT_NAME	TABLE_SCHEMA	TABLE_NAME	CONSTRAINT_TYPE
def	test	FK_9CA1B3534C397118	test	tblproducts	FOREIGN KEY
def	test	FK_1C5BFC7ABF396750	test	tblcontacts	FOREIGN KEY

I hope it helps you :)