WEEK 8

• SQL Constraints - These rules control the data that can be stored in a column
• NOT NULL CONSTRAINT - in a column means that the column cannot store NULL values
• UNIQUE CONSTRAINT - in a column means that the column must have unique value.
• PRIMARY KEY CONSTRAINT - is simply a combination of NOT NULL and UNIQUE constraints.
• FOREIGN KEY CONSTRAINT - in a column is used to reference a record that exists in another table.
• CHECK CONSTRAINT - checks the condition before allowing values in a table.
• DEFAULT CONSTRAINT - is used to set the default value if we try to store NULL in a column.
• CREATE INDEX CONSTRAINT - it's faster to retrieve data if we use that column for data retrieval.
• Cascading Referential Integrity Constraints - you can define the actions that the Database Engine takes when a user tries to delete or update a key
• NO ACTION - The Database Engine raises an error and the delete or update action on the row in the parent table is rolled back.
• CASCADE - Corresponding rows are updated or deleted in the referencing table when that row is updated or deleted in the parent table.
• SET NULL - All the values that make up the foreign key are set to NULL when the corresponding row in the parent table is updated or deleted.