ALTER TABLE
SQL - Language Statements
ALTER TABLE
Modifies table properties
1999-07-20
ALTER TABLE table
[ * ] ADD [ COLUMN ] column type
ALTER TABLE table
[ * ] RENAME [ COLUMN ] column TO newcolumn
ALTER TABLE table
RENAME TO newtable
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 an existing column.
1998-04-15
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.
1998-04-15
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.
1998-04-15
Notes
The keyword COLUMN is noise and can be omitted.
*
following a name of a table indicates that the statement
should be run over that table and all tables below it in the
inheritance hierarchy;
by default, the attribute will not be added to or renamed in any of the subclasses.
This should always be done when adding or modifying an attribute in a
superclass. If it is not, queries on the inheritance hierarchy
such as
SELECT NewColumn FROM SuperClass*
will not work because the subclasses will be missing an attribute
found in the superclass.
For efficiency reasons, default values for added attributes are
not placed in existing instances of a class.
That is, existing instances will have NULL values in the new
attributes. If non-NULL values are desired, a subsequent
UPDATE query
()
should be run.
You must own the class in order to change its schema.
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;
Compatibility
1998-04-15
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 >constrain> ] 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;