Contraints

• Unique
• Check
• Default
• Primary key
• Foreign key
• Not null

basic syntax

ALTER TABLE <table_name> ADD CONSTRAINT <constraint_name> TYPE;

sample unique constraint

ALTER TABLE <table_name> ADD CONSTRAINT <constraint_name> UNIQUE(<id_column>);

Validation

ALTER TABLE <table_name> ADD CONSTRAINT >constraint_name> CHECK(column_value > 0);

Drop constraint

ALTER TABLE <table_name> DROP CONSTRAINT <constraint_name>;

Drop constraint only if exists

ALTER TABLE <table_name> DROP CONSTRAINT IF EXISTS <constraint_name>;