Explain the two constraints, check and foreign key in SQL along with an example for each. Give the syntax.

CHECK constraint - CHECK constraint specifies an expression which must always be true for every row in the table. It can't refer to values within other rows.
Syntax:
ALTER TABLE
ADD CONSTRAINT CHECK();

FOREIGN KEY constraint - A foreign key is a combination of columns along with values based on the primary key values from another table. A foreign key constraint, also called as referential integrity constraint, specifies in which the values of the foreign key correspond to actual values of the primary or unique key in other table. One can refer to a primary or unique key in the similar table also.

Syntax:
ALTER TABLE
ADD CONSTRAINT FOREIGN KEY()
REFERENCES () ON {DELETE | UPDATE}
CASCADE;