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ALTER TABLE

Name

ALTER TABLE — Modifies table properties
ALTER TABLE table
    [ * ] ADD [ COLUMN ] column type
ALTER TABLE table
    [ * ] RENAME [ COLUMN ] column TO newcolumn
ALTER TABLE table
    RENAME TO newtable

Inputs

table

The name of an existing table to alter.

column

Name of a new or existing column.

type

Type of the new column.

newcolumn

New name for an existing column.

newtable

New name for an existing column.

Outputs

ALTER

Message returned from column or table renaming.

NEW

Message returned from column addition.

ERROR

Message returned if table or column is not available.

Description

ALTER TABLE changes the definition of an existing table. The new columns and their types are specified in the same style and with the the same restrictions as in CREATE TABLE. The RENAME clause causes the name of a table or column to change without changing any of the data contained in the affected table. Thus, the table or column will remain of the same type and size after this command is executed.

You must own the table in order to change its schema.

Notes

The keyword COLUMN is noise and can be omitted.

“[*]” following a name of a table indicates that statement should be run over that table and all tables below it in the inheritance hierarchy. The PostgreSQL User's Guide has further information on inheritance.

Refer to CREATE TABLE for a further description of valid arguments.

Usage

To add a column of type VARCHAR to a table:

    ALTER TABLE distributors ADD COLUMN address VARCHAR(30);

To rename an existing column:

    ALTER TABLE distributors RENAME COLUMN address TO city;

To rename an existing table:

    ALTER TABLE distributors RENAME TO suppliers;

Compatibility

SQL92

ALTER TABLE/RENAME is a Postgres language extension.

SQL92 specifies some additional capabilities for ALTER TABLE statement which are not yet directly supported by Postgres:

ALTER TABLE table ALTER [ COLUMN ] column
    SET DEFAULT default

ALTER TABLE table ALTER [ COLUMN ] column
    ADD [ CONSTRAINT constraint ] table-constraint

Puts the default value or constraint specified into the definition of column in the table. See CREATE TABLE for the syntax of the default and table-constraint clauses. If a default clause already exists, it will be replaced by the new definition. If any constraints on this column already exist, they will be retained using a boolean AND with the new constraint.

Currently, to set new default constraints on an existing column the table must be recreated and reloaded:

CREATE TABLE temp AS SELECT * FROM distributors;
DROP TABLE distributors;
CREATE TABLE distributors (
    did      DECIMAL(3) DEFAULT 1,
    name     VARCHAR(40) NOT NULL,
    city     VARCHAR(30)
);
INSERT INTO distributors SELECT * FROM temp;
DROP TABLE temp;
ALTER TABLE table
    DROP DEFAULT default
ALTER TABLE table
    DROP CONSTRAINT constraint { RESTRICT | CASCADE }

Removes the default value specified by default or the rule specified by constraint from the definition of a table. If RESTRICT is specified only a constraint with no dependent constraints can be destroyed. If CASCADE is specified, Any constraints that are dependent on this constraint are also dropped.

Currently, to remove a default value or constraints on an existing column the table must be recreated and reloaded:

CREATE TABLE temp AS SELECT * FROM distributors;
DROP TABLE distributors;
CREATE TABLE distributors AS SELECT * FROM temp;
DROP TABLE temp;
ALTER TABLE table
    DROP [ COLUMN ] column { RESTRICT | CASCADE }

Removes a column from a table. If RESTRICT is specified only a column with no dependent objects can be destroyed. If CASCADE is specified, all objects that are dependent on this column are also dropped.

Currently, to remove an existing column the table must be recreated and reloaded:

CREATE TABLE temp AS SELECT did, city FROM distributors;    
DROP TABLE distributors;
CREATE TABLE distributors (
    did      DECIMAL(3)  DEFAULT 1,
    name     VARCHAR(40) NOT NULL,
);
INSERT INTO distributors SELECT * FROM temp;
DROP TABLE temp;
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