ALTER TABLE
SQL - Language Statements
ALTER TABLE
change the definition of a table
1999-07-20
ALTER TABLE [ ONLY ] table [ * ]
ADD [ COLUMN ] column type [ column_constraint [ ... ] ]
ALTER TABLE [ ONLY ] table [ * ]
ALTER [ COLUMN ] column { SET DEFAULT value | DROP DEFAULT }
ALTER TABLE [ ONLY ] table [ * ]
ALTER [ COLUMN ] column SET STATISTICS integer
ALTER TABLE [ ONLY ] table [ * ]
RENAME [ COLUMN ] column TO newcolumn
ALTER TABLE table
RENAME TO newtable
ALTER TABLE table
ADD table constraint definition
ALTER TABLE [ ONLY ] table
DROP CONSTRAINT constraint { RESTRICT | CASCADE }
ALTER TABLE table
OWNER TO new owner
1998-04-15
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 the table.
table constraint definition
New table constraint for the table
New user
The user name of the new owner of the table.
1998-04-15
Outputs
ALTER
Message returned from column or table renaming.
ERROR
Message returned if table or column is not available.
1998-04-15
Description
ALTER TABLE changes the definition of an existing table.
The ADD COLUMN form adds a new column to the table
using the same syntax as .
The ALTER COLUMN SET/DROP DEFAULT forms
allow you to set or remove the default for the column. Note that defaults
only apply to subsequent INSERT commands; they do not
cause rows already in the table to change.
The ALTER COLUMN SET STATISTICS form allows you to
set the statistics-gathering target for subsequent
operations.
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.
The ADD table constraint definition clause
adds a new constraint to the table using the same syntax as .
The DROP CONSTRAINT constraint clause
drops all CHECK constraints on the table (and its children) that match constraint.
The OWNER clause changes the owner of the table to the user
new user.
You must own the table in order to change its schema.
1998-04-15
Notes
The keyword COLUMN is noise and can be omitted.
In the current implementation of ADD COLUMN,
default and NOT NULL clauses for the new column are not supported.
You can use the SET DEFAULT form
of ALTER TABLE to set the default later.
(You may also want to update the already existing rows to the
new default value, using .)
Currently only CHECK constraints can be dropped from a table. The RESTRICT
keyword is required, although dependencies are not checked. The CASCADE
option is unsupported. To remove a PRIMARY or UNIQUE constraint, drop the
relevant index using the command.
To remove FOREIGN KEY constraints you need to recreate
and reload the table, using other parameters to the
command.
For example, to drop all constraints on a table distributors:
CREATE TABLE temp AS SELECT * FROM distributors;
DROP TABLE distributors;
CREATE TABLE distributors AS SELECT * FROM temp;
DROP TABLE temp;
You must own the table in order to change it.
Changing any part of the schema of a system
catalog is not permitted.
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;
To add a check constraint to a table:
ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);
To remove a check constraint from a table and all its children:
ALTER TABLE distributors DROP CONSTRAINT zipchk;
To add a foreign key constraint to a table:
ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses(address) MATCH FULL;
To add a (multi-column) unique constraint to a table:
ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);
Compatibility
1998-04-15
SQL92
The ADD COLUMN form is compliant with the exception that
it does not support defaults and NOT NULL constraints, as explained above.
The ALTER COLUMN form is in full compliance.
SQL92 specifies some additional capabilities for ALTER TABLE
statement which are not yet directly supported by Postgres:
ALTER TABLE table DROP [ COLUMN ] column { RESTRICT | CASCADE }
Removes a column from a table.
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;
The clauses to rename columns and tables are Postgres
extensions from SQL92.