alter_table man page on aLinux

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       ALTER TABLE - change the definition of a table

       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 [ ... ] ]
	   ALTER [ COLUMN ] column TYPE type [ USING expression ]
	   ALTER [ COLUMN ] column SET DEFAULT expression
	   ALTER [ COLUMN ] column { SET | DROP } NOT NULL
	   ALTER [ COLUMN ] column SET STATISTICS integer
	   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
	   OWNER TO new_owner
	   SET TABLESPACE new_tablespace

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

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

	      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

	      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.

	      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.

	      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.

	      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‐

	      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)].

	      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 match‐
	      ing constraints will be dropped.

	      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‐

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

	      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.

	      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.

	      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‐

       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.

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

       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  col‐
       umns  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.)

       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 name for an existing column.

	      New name for the table.

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

	      New table constraint for the table.

	      Name of an existing constraint to drop.

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

	      Refuse  to drop the column or constraint if there are any depen‐
	      dent objects. This is the default behavior.

	      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.

	      The  index name on which the table should be marked for cluster‐

	      The user name of the new owner of the table.

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

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

       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 tempo‐
       rarily 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‐

       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
	       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;

       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	  2005-11-05			 ALTER TABLE()

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