On Apache/2.2.3 (Red Hat)
Under GNU General Public License
2009-12-24 04:33 @127.0.0.1 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)
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 ]
ENABLE REPLICA TRIGGER trigger_name
ENABLE ALWAYS TRIGGER trigger_name
DISABLE RULE rewrite_rule_name
ENABLE RULE rewrite_rule_name
ENABLE REPLICA RULE rewrite_rule_name
ENABLE ALWAYS RULE rewrite_rule_name
CLUSTER ON index_name
SET WITHOUT CLUSTER
SET WITHOUT OIDS
SET ( storage_parameter = value [, ... ] )
RESET ( storage_parameter [, ... ] )
INHERIT parent_table
NO INHERIT parent_table
OWNER TO new_owner
SET TABLESPACE new_tablespace
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. Indexes and table constraints involv-
ing 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 automatically converted to use the
new column type by reparsing the originally supplied expression. The
optional USING clause specifies how to compute the new column value from the
old; if omitted, 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 val-
ues only apply to subsequent INSERT commands; they do not cause rows already
in the table to change. Defaults can 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 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 in the documen-
tation.
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 substring 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 in 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 [ REPLICA | ALWAYS ] TRIGGER
These forms configure the firing of trigger(s) belonging to the table. A
disabled trigger is still known to the system, but is not executed 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 can disable or enable a single trigger specified by name, or
all triggers on the table, or only user triggers (this option excludes trig-
gers 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 executed. The trigger firing mechanism
is also affected by the configuration variable session_replication_role.
Simply enabled triggers will fire when the replication role is ''origin''
(the default) or ''local''. Triggers configured ENABLE REPLICA will only
fire if the session is in ''replica'' mode and triggers configured ENABLE
ALWAYS will fire regardless of the current replication mode.
DISABLE/ENABLE [ REPLICA | ALWAYS ] RULE
These forms configure the firing of rewrite rules belonging to the table. A
disabled rule is still known to the system, but is not applied during query
rewriting. The semantics are as for disabled/enabled triggers. This configu-
ration is ignored for ON SELECT rules, which are always applied in order to
keep views working even if the current session is in a non-default replica-
tion role.
CLUSTER
This form selects the default index for future CLUSTER [cluster(7)] opera-
tions. It does not actually re-cluster the table.
SET WITHOUT CLUSTER
This form removes the most recently used CLUSTER [cluster(7)] index specifi-
cation 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.
SET ( storage_parameter = value [, ... ] )
This form changes one or more storage parameters for the table. See CREATE
TABLE [create_table(7)] for details on the available parameters. Note that
the table contents will not be modified immediately by this command; depend-
ing on the parameter you might need to rewrite the table to get the desired
effects. That can be done with CLUSTER [cluster(7)] or one of the forms of
ALTER TABLE that forces a table rewrite.
Note: While CREATE TABLE allows OIDS to be specified in the WITH (stor-
age_parameter) syntax, ALTER TABLE does not treat OIDS as a storage parame-
ter.
RESET ( storage_parameter [, ... ] )
This form resets one or more storage parameters to their defaults. As with
SET, a table rewrite might be needed to update the table entirely.
INHERIT parent_table
This form adds the target table as a new child of the specified parent ta-
ble. Subsequently, queries against the parent will include records of the
target table. To be added as a child, the target table must already contain
all the same columns as the parent (it could have additional columns, too).
The columns must have matching data types, and if they have NOT NULL con-
straints in the parent then they must also have NOT NULL constraints in the
child.
There must also be matching child-table constraints for all CHECK con-
straints of the parent. Currently UNIQUE, PRIMARY KEY, and FOREIGN KEY con-
straints are not considered, but this might change in the future.
NO INHERIT parent_table
This form removes the target table from the list of children of the speci-
fied parent table. Queries against the parent table will no longer include
records drawn from the target table.
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 sepa-
rately with additional SET TABLESPACE commands. See also CREATE TABLESPACE
[create_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 table. There is no effect on the
stored data.
SET SCHEMA
This form moves the table into another schema. Associated indexes, con-
straints, and sequences owned by table columns are moved as well.
All the actions except RENAME and SET SCHEMA can be combined into a list of multi-
ple 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 par-
ticularly 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 add the table as a new child
of a parent table, you must own the parent table as well. To alter the owner, you
must also be a direct or indirect member of the new owning 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. However, 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 ta-
ble and all its descendant tables (if any) are updated. * can be appended to
the table name to indicate that descendant tables are to be altered, 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
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 dependent 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 supe-
ruser privilege if any of the triggers are for foreign 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 clustering.
storage_parameter
The name of a table storage parameter.
value The new value for a table storage parameter. This might be a number or a
word depending on the parameter.
parent_table
A parent table to associate or de-associate with this table.
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 initial-
ized 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 might take a significant amount
of time for a large table; and it will temporarily 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 sometimes an advan-
tage, 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 might fail to convert the default even though
a USING clause is supplied. In such cases, drop the default with DROP DEFAULT, per-
form the ALTER TYPE, and then use SET DEFAULT to add a suitable new default. Simi-
lar 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 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.
The TRIGGER, CLUSTER, OWNER, and TABLESPACE actions never recurse to descendant
tables; that is, they always act as though ONLY were specified. Adding a con-
straint 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 parame-
ters. in the documentation has further information on inheritance.
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';
The same, when the column has a default expression that won't automatically cast to
the new data type:
ALTER TABLE foo
ALTER COLUMN foo_timestamp DROP DEFAULT,
ALTER COLUMN foo_timestamp TYPE timestamp with time zone
USING
timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',
ALTER COLUMN foo_timestamp SET DEFAULT now();
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 ta-
ble 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 disallows zero-column tables.
SQL - Language Statements 2009-03-12 ALTER TABLE()
Generated by $Id: phpMan.php,v 4.54 2007/08/21 09:05:22 chedong Exp $ Author: Che Dong
On Apache/2.2.3 (Red Hat)
Under GNU General Public License
2009-12-24 04:33 @127.0.0.1 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)