Can y’all help me

Question

So I’m new in this and I’m using Phpmyadmin but how can I make my table check if the Person 1 is Equal to person 2 Like
Mike is the Brother of Mike this should be false
So I want to make a Constraint I heard I can do this with Check Where I only have to put
SELECT TABLE Blabla
CHECK (Person1 !=Person2);
But I don’t know
1. where to put this
and
2. How to make a Warning „ Mike can’t be his own brother“
I hope I could explain my Problem and you guys could help me

Answer 1

Are you looking for the where clause.
SELECT *
FROM sites
WHERE site_name = 'TechOnTheNet.com';
https://www.techonthenet.com/mariadb/where.php
SELECT *
FROM blabla
WHERE Person1 !=Person2;

Answer 2

thank yall for the help so I did now made a constraint
ALTER TABLE Person
ADD CONSTRAINT CHK_PERSON
CHECK(Person1ID<>Person2ID)
that should only accept valid relationships