| A | B |
|---|
| CASCADE Constraint | constraints referring to dropped columns will also be dropped. |
| REFERENCES | identifies that table and column in the parent table. |
| Column Level Constraint | references a single column and is defined within a specification for the owning column. |
| DISABLE CONSTRAINT | to deactivate an integrity constraint. |
| ON DELETE SET NULL | converts dependent foreign key values to null. |
| Table Level Constraint | references one or more columns and is defined separately from the definitions of the columns in the table. |
| ENABLE CONSTRAINT | to activate an integrity constraint currently disabled |
| NOT NULL | constraint ensures that the column contains no null values |
| UNIQUE KEY | an integrity constraint that requires every value in a column or set of columns be unique. |
| FOREIGN KEY | designates a column (child table) that establishes a relationship between a primary key in the same table and a different table (parent table). |
| ON DELETE CASCADE | deletes the dependent rows in the child table when a row in the parent table is deleted. |
| DROP CONSTRAINT | removes a constraint from a table. |
| PRIMARY KEY | constraint ensures that the column contains no null values and uniquely identifies each row of the table. |
| Constraints | enforces rules on the data in a table. |
| CHECK Constraint | specifies a condition that must be true for each row of data. |
