Constraints and enforcement

The remainder of this chapter deals with table constraints, so it is necessary to understand what they are and to mention several important details regarding their use in Snowflake. In the ANSI-SQL standard, constraints define integrity and consistency rules for data stored in tables. Snowflake supports four constraint types:

• PRIMARY KEY
• UNIQUE
• FOREIGN KEY
• NOT NULL

Since the function of each of these constraints is covered later in this chapter, this section will be limited to their enforcement.

Enforcement, on the part of the database, means actively monitoring the integrity rules of a given constraint when DML operations are performed on a table. By enforcing a constraint, a database ensures that an error is raised when the constraint is violated, and the offending DML operation is not allowed to complete.

For example, a NOT NULL constraint on a column indicates that this column cannot contain NULL values. By enforcing...