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ALTER TABLE()			 SQL Commands			 ALTER TABLE()



NAME
       ALTER TABLE - change the definition of a table


SYNOPSIS
       ALTER TABLE [ ONLY ] name [ * ]
	   action [, ... ]
       ALTER TABLE [ ONLY ] name [ * ]
	   RENAME [ COLUMN ] column TO new_column
       ALTER TABLE name
	   RENAME TO new_name
       ALTER TABLE name
	   SET SCHEMA new_schema

       where action is one of:

	   ADD [ COLUMN ] column type [ column_constraint [ ... ] ]
	   DROP [ COLUMN ] column [ RESTRICT | CASCADE ]
	   ALTER [ COLUMN ] column TYPE type [ USING expression ]
	   ALTER [ COLUMN ] column SET DEFAULT expression
	   ALTER [ COLUMN ] column DROP DEFAULT
	   ALTER [ COLUMN ] column { SET | DROP } NOT NULL
	   ALTER [ COLUMN ] column SET STATISTICS integer
	   ALTER [ COLUMN ] column SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
	   ADD table_constraint
	   DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ]
	   DISABLE TRIGGER [ trigger_name | ALL | USER ]
	   ENABLE TRIGGER [ trigger_name | ALL | USER ]
	   CLUSTER ON index_name
	   SET WITHOUT CLUSTER
	   SET WITHOUT OIDS
	   OWNER TO new_owner
	   SET TABLESPACE new_tablespace


DESCRIPTION
       ALTER  TABLE  changes  the  definition of an existing table.  There are
       several subforms:

       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. Indexes and table con-
	      straints 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  or
	      views.

       ALTER COLUMN TYPE
	      This  form  changes the type of a column of a table. Indexes and
	      simple table constraints involving the column will be  automati-
	      cally  converted	to  use	 the  new column type by reparsing the
	      originally supplied expression. The optional USING clause speci-
	      fies  how to compute the new column value from the old; if omit-
	      ted, the default conversion is the same as  an  assignment  cast
	      from  old	 data  type to new. A USING clause must be provided if
	      there is no implicit or assignment cast from old to new type.

       SET/DROP DEFAULT
	      These forms set or remove the default value for a	 column.   The
	      default values 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 val-
	      ues or to reject null values. You can only use SET NOT NULL when
	      the column contains no null values.

       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
	      (default_statistics_target).  For more information on the use of
	      statistics by the PostgreSQL query planner, refer to  the	 docu-
	      mentation.


       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 most data types
	      that support non-PLAIN storage.  Use of EXTERNAL will make  sub-
	      string  operations  on  text  and	 bytea	columns faster, at the
	      penalty of  increased  storage  space.  Note  that  SET  STORAGE
	      doesn't  itself  change  anything in the table, it just sets the
	      strategy to be pursued during future  table  updates.   See  the
	      documentation for more information.

       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 the specified constraint on a table.

       DISABLE/ENABLE TRIGGER
	      These forms disable or enable trigger(s) belonging to the table.
	      A disabled trigger is still known to the system, but is not exe-
	      cuted when its triggering event occurs. For a deferred  trigger,
	      the enable status is checked when the event occurs, not when the
	      trigger function is actually executed. One may disable or enable
	      a	 single	 trigger specified by name, or all triggers on the ta-
	      ble, or only user triggers (this option excludes	triggers  that
	      are  used	 to  implement	foreign key constraints). Disabling or
	      enabling constraint triggers requires superuser  privileges;  it
	      should be done with caution since of course the integrity of the
	      constraint cannot be guaranteed if the  triggers	are  not  exe-
	      cuted.

       CLUSTER
	      This  form  selects  the default index for future CLUSTER [clus-
	      ter(7)] operations. It does not actually re-cluster the table.

       SET WITHOUT CLUSTER
	      This form removes the most recently  used	 CLUSTER  [cluster(7)]
	      index  specification from the table. This affects future cluster
	      operations that don't specify an index.

       SET WITHOUT OIDS
	      This form removes the oid system column from the table. This  is
	      exactly  equivalent  to DROP COLUMN oid RESTRICT, except that it
	      will not complain if there is already no oid column.

	      Note that there is no variant of ALTER TABLE that allows OIDs to
	      be restored to a table once they have been removed.

       OWNER  This  form  changes the owner of the table, sequence, or view to
	      the specified user.

       SET TABLESPACE
	      This form	 changes  the  table's	tablespace  to	the  specified
	      tablespace  and moves the data file(s) associated with the table
	      to the new tablespace.  Indexes on the table, if	any,  are  not
	      moved;  but  they	 can  be  moved separately with additional SET
	      TABLESPACE  commands.   See   also   CREATE   TABLESPACE	 [cre-
	      ate_tablespace(7)].

       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  ta-
	      ble. There is no effect on the stored data.

       SET SCHEMA
	      This  form  moves	 the  table  into  another  schema. Associated
	      indexes, constraints, and SERIAL-column sequences are  moved  as
	      well.


       All  the	 actions  except  RENAME and SET SCHEMA can be combined into a
       list of multiple alterations to apply in parallel. For example,	it  is
       possible	 to  add  several  columns  and/or  alter  the type of several
       columns in a single command. This is  particularly  useful  with	 large
       tables, since only one pass over the table need be made.

       You  must  own the table to use ALTER TABLE.  To change the schema of a
       table, you must also have CREATE privilege on the new schema.  To alter
       the owner, you must also be a direct or indirect member of the new own-
       ing role, and that role must  have  CREATE  privilege  on  the  table's
       schema.	(These restrictions enforce that altering the owner doesn't do
       anything you couldn't do by dropping and recreating  the	 table.	  How-
       ever, a superuser can alter ownership of any table anyway.)

PARAMETERS
       name   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	 indi-
	      cate  that  descendant tables are to be altered, but in the cur-
	      rent version, this is the default behavior. (In releases	before
	      7.1,  ONLY  was the default behavior. The default can be altered
	      by changing the configuration parameter sql_inheritance.)

       column Name of a new or existing column.

       new_column
	      New name for an existing column.

       new_name
	      New name for the table.

       type   Data type of the new column, or new data type  for  an  existing
	      column.

       table_constraint
	      New table constraint for the table.

       constraint_name
	      Name of an existing constraint to drop.

       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	depen-
	      dent objects. This is the default behavior.

       trigger_name
	      Name of a single trigger to disable or enable.

       ALL    Disable  or  enable  all triggers belonging to the table.	 (This
	      requires superuser privilege if any of the triggers are for for-
	      eign key constraints.)

       USER   Disable or enable all triggers belonging to the table except for
	      foreign key constraint triggers.

       index_name
	      The index name on which the table should be marked for  cluster-
	      ing.

       new_owner
	      The user name of the new owner of the table.

       new_tablespace
	      The name of the tablespace to which the table will be moved.

       new_schema
	      The name of the schema to which the table will be moved.

NOTES
       The key word COLUMN is noise and can be omitted.

       When  a column is added with ADD COLUMN, all existing rows in the table
       are initialized with the column's default value	(NULL  if  no  DEFAULT
       clause is specified).

       Adding  a  column  with	a  non-null default or changing the type of an
       existing column will require the entire table to be rewritten. This may
       take  a	significant amount of time for a large table; and it will tem-
       porarily require double the disk space.

       Adding a CHECK or NOT NULL constraint requires scanning	the  table  to
       verify that existing rows meet the constraint.

       The main reason for providing the option to specify multiple changes in
       a single ALTER TABLE is that  multiple  table  scans  or	 rewrites  can
       thereby be combined into a single pass over the table.

       The  DROP COLUMN form does not physically remove the column, but simply
       makes it invisible to SQL  operations.  Subsequent  insert  and	update
       operations  in  the table will store a null value 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.

       The  fact  that	ALTER TYPE requires rewriting the whole table is some-
       times an advantage, because the rewriting process eliminates  any  dead
       space  in  the  table.  For example, to reclaim the space occupied by a
       dropped column immediately, the fastest way is

       ALTER TABLE table ALTER COLUMN anycol TYPE anytype;

       where anycol is any remaining table column and anytype is the same type
       that  column  already  has.   This  results  in no semantically-visible
       change in the table, but the command forces rewriting, which  gets  rid
       of no-longer-useful data.

       The  USING  option  of  ALTER  TYPE can actually specify any expression
       involving the old values of the row; that is, it	 can  refer  to	 other
       columns	as  well  as the one being converted. This allows very general
       conversions to be done with the ALTER  TYPE  syntax.  Because  of  this
       flexibility,  the  USING	 expression  is	 not  applied  to the column's
       default value (if any); the result might not be a  constant  expression
       as  required  for a default.  This means that when there is no implicit
       or assignment cast from old to new type, ALTER TYPE may fail to convert
       the default even though a USING clause is supplied. In such cases, drop
       the default with DROP DEFAULT, perform the ALTER TYPE, and then use SET
       DEFAULT	to add a suitable new default. Similar considerations apply to
       indexes and constraints involving the column.

       If a table has any descendant tables,  it  is  not  permitted  to  add,
       rename,	or  change  the	 type  of 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 match-
       ing the parent.

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

       The  TRIGGER,  CLUSTER,	OWNER, and TABLESPACE actions never recurse to
       descendant tables; that is, they always act as though ONLY were	speci-
       fied.  Adding a constraint can recurse only for CHECK constraints.

       Changing any part of a system catalog table is not permitted.

       Refer  to  CREATE  TABLE [create_table(7)] for a further description of
       valid parameters. the documentation has further information on  inheri-
       tance.

EXAMPLES
       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 change the types of two existing columns in one operation:

       ALTER TABLE distributors
	   ALTER COLUMN address TYPE varchar(80),
	   ALTER COLUMN name TYPE varchar(100);


       To  change  an  integer	column containing UNIX timestamps to timestamp
       with time zone via a USING clause:

       ALTER TABLE foo
	   ALTER COLUMN foo_timestamp TYPE timestamp with time zone
	   USING
	       timestamp with time zone 'epoch' + foo_timestamp * interval '1 second';


       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);


       To move a table to a different tablespace:

       ALTER TABLE distributors SET TABLESPACE fasttablespace;


       To move a table to a different schema:

       ALTER TABLE myschema.distributors SET SCHEMA yourschema;


COMPATIBILITY
       The ADD, DROP, and SET DEFAULT forms conform with the SQL standard. The
       other forms are PostgreSQL extensions of the SQL standard.   Also,  the
       ability	to  specify more than one manipulation in a single ALTER TABLE
       command is an extension.

       ALTER TABLE DROP COLUMN can be used to drop the only column of a table,
       leaving	a zero-column table. This is an extension of SQL, which disal-
       lows zero-column tables.



SQL - Language Statements	  2010-12-14			 ALTER TABLE()
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