ALTER 
TABLE(7)							   SQL Commands 						    ALTER TABLE(7)

NAME

       ALTER TABLE - change the definition of a table

SYNOPSIS

       ALTER TABLE [ ONLY ] table [ * ]
	   ADD [ COLUMN ] column type [ column_constraint [ ... ] ]
       ALTER TABLE [ ONLY ] table [ * ]
	   DROP [ COLUMN ] column [ RESTRICT | CASCADE ]
       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 [ ONLY ] table [ * ]
	   ADD table_constraint
       ALTER TABLE [ ONLY ] table [ * ]
	   DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ]
       ALTER TABLE table
	   OWNER TO new_owner

   INPUTS
       table  The name (possibly schema-qualified) of an existing table to alter. If ONLY is specified, only that table is altered. If ONLY is not
	      specified, the table and all its descendant tables (if any) are updated. * can be appended  to  the  table  name	to  indicate  that
	      descendant tables are to be scanned, but in the current version, this is the default behavior. (In releases before 7.1, ONLY was the
	      default behavior.) The default can be altered by changing the SQL_INHERITANCE configuration option.

       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
	      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.

       CASCADE
	      Automatically drop objects that depend on the dropped column or constraint (for example, views referencing the column).

       RESTRICT
	      Refuse to drop the column or constraint if there are any dependent objects. This is the default behavior.

   OUTPUTS
       ALTER TABLE
	      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.  There are several sub-forms:

       ADD COLUMN
	      This form adds a new column to the table using the same syntax as CREATE TABLE [create_table(7)].

       DROP COLUMN
	      This form drops a column from a table. Note that indexes and table constraints involving the column will be automatically dropped as
	      well.  You  will	need  to  say CASCADE if anything outside the table depends on the column --- for example, foreign key references,
	      views, etc.

       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  ta-
	      ble contains no null values in the column.

       SET STATISTICS
	      This  form sets the per-column statistics-gathering target for subsequent ANALYZE [analyze(7)] operations.  The target can be set in
	      the range 0 to 1000; alternatively, set it to -1 to revert to using the system default statistics target.

       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, uncom-
	      pressed. 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 data types that support it. The use of EXTERNAL will make substring operations on a TEXT col-
	      umn 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
	      This form adds a new constraint to a table using the same syntax as CREATE TABLE [create_table(7)].

       DROP CONSTRAINT
	      This  form  drops  constraints  on a table.  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.

   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.   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 UPDATE [update(7)].)  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.

       The  DROP  COLUMN  command  does  not physically remove the column, but simply makes it invisible to SQL operations. Subsequent inserts and
       updates of the table will store a NULL for the column.  Thus, dropping a column is quick but it will not  immediately  reduce  the  on-disk
       size  of  your  table, as the space occupied by the dropped column is not reclaimed. The space will be reclaimed over time as existing rows
       are updated.  To reclaim the space at once, do a dummy UPDATE of all rows and then vacuum, as in:

       UPDATE table SET col = col;
       VACUUM FULL table;

       If a table has any descendant tables, it is not permitted to ADD or RENAME a column in the parent table	without  doing	the  same  to  the
       descendants --- that is, ALTER TABLE ONLY will be rejected. This ensures that the descendants always have columns matching the parent.

       A  recursive  DROP  COLUMN  operation  will remove a descendant table's column only if the descendant does not inherit that column from any
       other parents and never had an independent definition of the column.  A nonrecursive DROP COLUMN (i.e., ALTER TABLE ONLY ...  DROP  COLUMN)
       never removes any descendant columns, but instead marks them as independently defined rather than inherited.

       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.

USAGE

       To add a column of type varchar to a table:

       ALTER TABLE distributors ADD COLUMN address VARCHAR(30);

       To drop a column from a table:

       ALTER TABLE distributors DROP COLUMN address RESTRICT;

       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;

       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);

COMPATIBILITY

   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.

       The clauses to rename tables, columns, indexes, and sequences are PostgreSQL extensions from SQL92.

SQL - Language Statements					    2002-11-22							    ALTER TABLE(7)