ALTER TABLE() SQL Commands ALTER TABLE()NAME
ALTER TABLE - Modifies table properties
SYNOPSIS
ALTER TABLE [ ONLY ] table [ * ]
ADD [ COLUMN ] column type
ALTER TABLE [ ONLY ] table [ * ]
ALTER [ COLUMN ] column { SET DEFAULT value | DROP DEFAULT }
ALTER TABLE table [ * ]
RENAME [ COLUMN ] column TO newcolumn
ALTER TABLE table
RENAME TO newtable
ALTER TABLE table
ADD table constraint definition
ALTER TABLE table
OWNER TO new owner
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.
OUTPUTS
ALTER Message returned from column or table renaming.
ERROR Message returned if table or column is not available.
DESCRIPTION
ALTER TABLE changes the definition of an existing table. The ADD COL‐
UMN form adds a new column to the table using the same syntax as CREATE
TABLE [create_table(l)]. The ALTER COLUMN form allows you to set or
remove the default for the column. Note that defaults only apply to
newly inserted rows. 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 def‐
inition clause adds a new constraint to the table using the same syntax
as CREATE TABLE [create_table(l)]. The OWNER clause chnages the owner
of the table to the user new user.
You must own the table in order to change its schema.
NOTES
The keyword COLUMN is noise and can be omitted.
In the current implementation, default and constraint clauses for the
new column will be ignored. You can use the SET DEFAULT form of ALTER
TABLE to set the default later. (You will also have to update the
already existing rows to the new default value, using UPDATE
[update(l)].)
In the current implementation, only FOREIGN KEY constraints can be
added to a table. To create or remove a unique constraint, create a
unique index (see CREATE INDEX [create_index(l)]). To add check con‐
straints you need to recreate and reload the table, using other parame‐
ters to the CREATE TABLE [create_table(l)] command.
You must own the table in order to change it. Renaming 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 foreign key constraint to a table:
ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses(address) MATCH FULL
COMPATIBILITY
SQL92
The ADD COLUMN form is compliant with the exception that it does not
support defaults and 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:
.sp Removes a table constraint (such as a check constraint, unique
constraint, or foreign key constraint). To remove a unique con‐
straint, drop a unique index. To remove other kinds of con‐
straints you need to recreate and reload the table, using other
parameters to the CREATE TABLE [create_table(l)] command.
For example, to drop any 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;
.sp 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.
SQL - Language Statements 29 March 2001 ALTER TABLE()
