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Table constraints
Syntax
SQL Compliance
Progress Software Corporation specific extension.
Related statements
ALTER TABLE, CREATE INDEX, CREATE TABLE
Table constraints
Specifies a constraint for a table that restricts the values that the table can store. INSERT, UPDATE,
or DELETE statements that violate the constraint fail. SQL returns a constraint violation error.
Table constraints have syntax and behavior similar to column constraints. Note the following
differences:
• The definitions of the table constraints are separated from the column definitions by
commas.
• Table constraint definitions can include more than one column, and SQL evaluates the
constraint based on the combination of values stored in all the columns.
CONSTRAINT constraint_name
PRIMARY KEY ( column [ , ... ] )
| UNIQUE ( column [ , ... ] )
| FOREIGN KEY ( column [, ... ] )
REFERENCES [ owner_name.]table_name [ ( column [ , ... ] ) ]
| CHECK ( search_condition )
CONSTRAINT constraint_name
Allows you to assign a name that you choose to the table constraint. While this
specification is optional, this facilitates making changes to the table definition, since the
name you specify is in your source CREATE TABLE statement. If you do not specify a
constraint_name, the database assigns a name. These names can be long and unwieldy,
and you must query system tables to determine the name.
PRIMARY KEY ( column [ , ... ] )
Defines the column list as the primary key for the table. There can be at most one primary
key for a table.
All the columns that make up a table level primary key must be defined as NOT NULL, or the
CREATE TABLE statement fails. The combination of values in the columns that make up the
primary key must be unique for each row in the table.
Other tables can name primary keys in their REFERENCES clauses. If they do, SQL restricts
operations on the table containing the primary key in the following ways:
• DROP TABLE statements that delete the table fail
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