An assertion is a predicate expressing a condition that we wish the

database always to satisfy.

$$ The following constraints, can be expressed using assertions:

$$ For each tuple in the student relation, the value of the attribute tot$\_$cred

must equal the sum of credits of courses that the student has completed

successfully.

$$ An instructor cannot teach in two different classrooms in a semester in the

same time slot

$$ An assertion in SQL takes the form:

create assertion check $()$; explain it