Table-Constraint

Adds a constraint to table metadata. You can specify table constraints with CREATE TABLE, or add a constraint to an existing table with ALTER TABLE. For details, see Setting Constraints in the Administrator's Guide.

Adding a constraint to a table that is referenced in a view does not affect the view.

Syntax

[ CONSTRAINT constraint-name ]
{
... PRIMARY KEY (column[,... ]) [ ENABLED | DISABLED ]
... | FOREIGN KEY (column[,... ] ) REFERENCES table [ (column[,...]) ]
... | UNIQUE (column[,...]) [ ENABLED | DISABLED ]
... | CHECK (expression) [ ENABLED | DISABLED ]
}

Parameters

`CONSTRAINT constraint‑name`	Assigns a name to the constraint. Vertica recommends that you name all constraints.
`PRIMARY KEY`	Defines one or more `NOT NULL` columns as the primary key as follows: PRIMARY KEY (column[,...]) [ ENABLED \| DISABLED] You can qualify this constraint with the keyword `ENABLED` or `DISABLED`. See Enforcing Constraints below. If you do not name a primary key constraint, Vertica assigns the name `C_PRIMARY`.
`FOREIGN KEY`	Adds a referential integrity constraint defining one or more columns as foreign keys as follows: FOREIGN KEY (column[,... ]) REFERENCES table [(column[,... ])] If you omit column, Vertica references the primary key in table. If you do not name a foreign key constraint, Vertica assigns the name `C_FOREIGN`. Adding a foreign key constraint requires the following privileges (in addition to privileges also required by ALTER TABLE): REFERENCES on the referenced table USAGE on the schema of the referenced table
`UNIQUE`	Specifies that the data in a column or group of columns is unique with respect to all table rows, as follows: UNIQUE (column[,...]) [ENABLED \| DISABLED] You can qualify this constraint with the keyword `ENABLED` or `DISABLED`. See Enforcing Constraints below. If you do not name a unique constraint, Vertica assigns the name `C_UNIQUE`.
`CHECK`	Specifies a check condition as an expression that returns a Boolean value, as follows: CHECK (expression) [ENABLED \| DISABLED] You can qualify this constraint with the keyword `ENABLED` or `DISABLED`. See Enforcing Constraints below. If you do not name a check constraint, Vertica assigns the name `C_CHECK`.

Privileges

Non-superusers: table owner, or the following privileges:

USAGE on schema
ALTER on table
SELECT on table to enable or disable constraint enforcement

Enforcing Constraints

A table can specify whether Vertica automatically enforces a primary key, unique key or check constraint with the keyword ENABLED or DISABLED. If you omit ENABLED or DISABLED, Vertica determines whether to enable the constraint automatically by checking the appropriate configuration parameter:

EnableNewPrimaryKeysByDefault
EnableNewUniqueKeysByDefault
EnableNewCheckConstraintsByDefault

For details, see Constraint Enforcement.

Examples

The following example creates a table (t01) with a primary key constraint.

CREATE TABLE t01 (id int CONSTRAINT sampleconstraint PRIMARY KEY);
CREATE TABLE

This example creates the same table without the constraint, and then adds the constraint with ALTER TABLE ADD CONSTRAINT

CREATE TABLE t01 (id int);
CREATE TABLE

ALTER TABLE t01 ADD CONSTRAINT sampleconstraint PRIMARY KEY(id);
WARNING 2623:  Column "id" definition changed to NOT NULL
ALTER TABLE

The following example creates a table (addapk) with two columns, adds a third column to the table, and then adds a primary key constraint on the third column.

=> CREATE TABLE addapk (col1 INT, col2 INT);
CREATE TABLE

=> ALTER TABLE addapk ADD COLUMN col3 INT;
ALTER TABLE

=> ALTER TABLE addapk ADD CONSTRAINT col3constraint PRIMARY KEY (col3) ENABLED;
WARNING 2623:  Column "col3" definition changed to NOT NULL
ALTER TABLE

Using the sample table addapk, check that the primary key constraint is enabled (is_enabled is t).

=> SELECT constraint_name, column_name, constraint_type, is_enabled FROM PRIMARY_KEYS WHERE table_name IN ('addapk');

 constraint_name | column_name | constraint_type | is_enabled
-----------------+-------------+-----------------+------------
 col3constraint  | col3        | p               | t
(1 row)

This example disables the constraint using ALTER TABLE ALTER CONSTRAINT.

=> ALTER TABLE addapk ALTER CONSTRAINT col3constraint DISABLED;

Check that the primary key is now disabled (is_enabled is f).

=> SELECT constraint_name, column_name, constraint_type, is_enabled FROM PRIMARY_KEYS WHERE table_name IN ('addapk');

 constraint_name | column_name | constraint_type | is_enabled
-----------------+-------------+-----------------+------------
 col3constraint  | col3        | p               | f
(1 row)