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 | DROP } NOT NULL ALTER TABLE [ ONLY ] table [ * ] ALTER [ COLUMN ] column SET STATISTICS integer ALTER TABLE [ ONLY ] table [ * ] ALTER [ COLUMN ] column SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN } ALTER TABLE [ ONLY ] table [ * ] RENAME [ COLUMN ] column TO new_column ALTER TABLE table RENAME TO new_table ALTER TABLE table ADD table_constraint_definition ALTER TABLE [ ONLY ] table DROP CONSTRAINT constraint_name { RESTRICT | CASCADE } ALTER TABLE table OWNER TO new_owner 1998-04-15 table The name (possibly schema-qualified) of an existing table to alter. column Name of a new or existing column. type Type of the new column. new_column New name for an existing column. new_table New name for the table. table_constraint_definition New table constraint for the table. constraint_name Name of an existing constraint to drop. new_owner The user name of the new owner of the table. 1998-04-15 ALTER Message returned from column or table renaming. ERROR Message returned if table or column is not available. 1998-04-15 ALTER TABLE changes the definition of an existing table. There are several sub-forms: ADD COLUMN This form adds a new column to the table using the same syntax as . SET/DROP DEFAULT These forms set or remove the default value for a column. Note that defaults only apply to subsequent INSERT commands; they do not cause rows already in the table to change. Defaults may also be created for views, in which case they are inserted into INSERT statements on the view before the view's ON INSERT rule is applied. SET/DROP NOT NULL These forms change whether a column is marked to allow NULL values or to reject NULL values. You may only SET NOT NULL when the table contains no NULLs in the column. SET STATISTICS This form sets the per-column statistics-gathering target for subsequent operations. SET STORAGE This form sets the storage mode for a column. This controls whether this column is held inline or in a supplementary table, and whether the data should be compressed or not. PLAIN must be used for fixed-length values such as INTEGER and is inline, uncompressed. MAIN is for inline, compressible data. EXTERNAL is for external, uncompressed data and EXTENDED is for external, compressed data. EXTENDED is the default for all datatypes that support it. The use of EXTERNAL will make substring operations on a TEXT column faster, at the penalty of increased storage space. RENAME The RENAME forms change the name of a table (or an index, sequence, or view) or the name of an individual column in a table. There is no effect on the stored data. ADD table_constraint_definition This form adds a new constraint to a table using the same syntax as . DROP CONSTRAINT This form drops constraints on a table (and its children). Currently, constraints on tables are not required to have unique names, so there may be more than one constraint matching the specified name. All such constraints will be dropped. OWNER This form changes the owner of the table, index, sequence or view to the specified user. You must own the table to use ALTER TABLE; except for ALTER TABLE OWNER, which may only be executed by a superuser. 1998-04-15 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. The new column always comes into being with all values NULL. You can use the SET DEFAULT form of ALTER TABLE to set the default afterwards. (You may also want to update the already existing rows to the new default value, using .) If you want to mark the column non-null, use the SET NOT NULL form after you've entered non-null values for the column in all rows. In DROP CONSTRAINT, the RESTRICT keyword is required, although dependencies are not yet checked. The CASCADE option is unsupported. Currently DROP CONSTRAINT only handles CHECK constraints. 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; Changing any part of the schema of a system catalog is not permitted. Refer to CREATE TABLE for a further description of valid arguments. The PostgreSQL User's Guide has further information on inheritance. 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 NOT NULL constraint to a column: ALTER TABLE distributors ALTER COLUMN street SET NOT NULL; To remove a NOT NULL constraint from a column: ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL; 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 RESTRICT; 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 (multicolumn) unique constraint to a table: ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode); To add an automatically named primary key constraint to a table, noting that a table can only ever have one primary key: ALTER TABLE distributors ADD PRIMARY KEY (dist_id); 1998-04-15 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 PostgreSQL: 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 tables, columns, indexes, and sequences are PostgreSQL extensions from SQL92.