Data Integrity

• Primary key 

• The primary key column cannot contain a null or empty value.

• The primary key column value must be unique.

• Each table can have only one primary key.

• Foreign key

• Referential integrity Constraint.

• In the parent-child relationship, the parent table keep the initial column values, and the child table's column values reference the parent column values.

• We have five different referential options - SET DEFAULT, SET NULL, CASCADE, NO ACTION, RESTRICT.

• CHECK constraint – add logic to check value based on a Boolean expression.

• UNIQUE constraint – make sure that values in a column or a group of columns unique across the table.

• NOT NULL constraint – ensure values in a column are not NULL.

• Explicit Locks, Advisory Locks