ALTER TABLE(7) PostgreSQL 15.7 Documentation ALTER TABLE(7)
NAME
ALTER_TABLE - change the definition of a table
SYNOPSIS
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
action [, ... ]
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
RENAME [ COLUMN ] column_name TO new_column_name
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
RENAME CONSTRAINT constraint_name TO new_constraint_name
ALTER TABLE [ IF EXISTS ] name
RENAME TO new_name
ALTER TABLE [ IF EXISTS ] name
SET SCHEMA new_schema
ALTER TABLE ALL IN TABLESPACE name [ OWNED BY role_name [, ... ] ]
SET TABLESPACE new_tablespace [ NOWAIT ]
ALTER TABLE [ IF EXISTS ] name
ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }
ALTER TABLE [ IF EXISTS ] name
DETACH PARTITION partition_name [ CONCURRENTLY | FINALIZE ]
where action is one of:
ADD [ COLUMN ] [ IF NOT EXISTS ] column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ]
ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type [ COLLATE collation ] [ USING expression ]
ALTER [ COLUMN ] column_name SET DEFAULT expression
ALTER [ COLUMN ] column_name DROP DEFAULT
ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL
ALTER [ COLUMN ] column_name DROP EXPRESSION [ IF EXISTS ]
ALTER [ COLUMN ] column_name ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ]
ALTER [ COLUMN ] column_name { SET GENERATED { ALWAYS | BY DEFAULT } | SET sequence_option | RESTART [ [ WITH ] restart ] } [...]
ALTER [ COLUMN ] column_name DROP IDENTITY [ IF EXISTS ]
ALTER [ COLUMN ] column_name SET STATISTICS integer
ALTER [ COLUMN ] column_name SET ( attribute_option = value [, ... ] )
ALTER [ COLUMN ] column_name RESET ( attribute_option [, ... ] )
ALTER [ COLUMN ] column_name SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
ALTER [ COLUMN ] column_name SET COMPRESSION compression_method
ADD table_constraint [ NOT VALID ]
ADD table_constraint_using_index
ALTER CONSTRAINT constraint_name [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
VALIDATE CONSTRAINT constraint_name
DROP CONSTRAINT [ IF EXISTS ] 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
DISABLE ROW LEVEL SECURITY
ENABLE ROW LEVEL SECURITY
FORCE ROW LEVEL SECURITY
NO FORCE ROW LEVEL SECURITY
CLUSTER ON index_name
SET WITHOUT CLUSTER
SET WITHOUT OIDS
SET ACCESS METHOD new_access_method
SET TABLESPACE new_tablespace
SET { LOGGED | UNLOGGED }
SET ( storage_parameter [= value] [, ... ] )
RESET ( storage_parameter [, ... ] )
INHERIT parent_table
NO INHERIT parent_table
OF type_name
NOT OF
OWNER TO { new_owner | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
REPLICA IDENTITY { DEFAULT | USING INDEX index_name | FULL | NOTHING }
and partition_bound_spec is:
IN ( partition_bound_expr [, ...] ) |
FROM ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] )
TO ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] ) |
WITH ( MODULUS numeric_literal, REMAINDER numeric_literal )
and column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL |
NULL |
CHECK ( expression ) [ NO INHERIT ] |
DEFAULT default_expr |
GENERATED ALWAYS AS ( generation_expr ) STORED |
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] |
UNIQUE [ NULLS [ NOT ] DISTINCT ] index_parameters |
PRIMARY KEY index_parameters |
REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and table_constraint is:
[ CONSTRAINT constraint_name ]
{ CHECK ( expression ) [ NO INHERIT ] |
UNIQUE [ NULLS [ NOT ] DISTINCT ] ( column_name [, ... ] ) index_parameters |
PRIMARY KEY ( column_name [, ... ] ) index_parameters |
EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters [ WHERE ( predicate ) ] |
FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and table_constraint_using_index is:
[ CONSTRAINT constraint_name ]
{ UNIQUE | PRIMARY KEY } USING INDEX index_name
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
index_parameters in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are:
[ INCLUDE ( column_name [, ... ] ) ]
[ WITH ( storage_parameter [= value] [, ... ] ) ]
[ USING INDEX TABLESPACE tablespace_name ]
exclude_element in an EXCLUDE constraint is:
{ column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
referential_action in a FOREIGN KEY/REFERENCES constraint is:
{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( column_name [, ... ] ) ] | SET DEFAULT [ ( column_name [, ... ] ) ] }
DESCRIPTION
ALTER TABLE changes the definition of an existing table. There are
several subforms described below. Note that the lock level required may
differ for each subform. An ACCESS EXCLUSIVE lock is acquired unless
explicitly noted. When multiple subcommands are given, the lock
acquired will be the strictest one required by any subcommand.
ADD COLUMN [ IF NOT EXISTS ]
This form adds a new column to the table, using the same syntax as
CREATE TABLE. If IF NOT EXISTS is specified and a column already
exists with this name, no error is thrown.
DROP COLUMN [ IF EXISTS ]
This form drops a column from a table. Indexes and table
constraints involving the column will be automatically dropped as
well. Multivariate statistics referencing the dropped column will
also be removed if the removal of the column would cause the
statistics to contain data for only a single column. You will need
to say CASCADE if anything outside the table depends on the column,
for example, foreign key references or views. If IF EXISTS is
specified and the column does not exist, no error is thrown. In
this case a notice is issued instead.
SET DATA 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 COLLATE clause specifies a
collation for the new column; if omitted, the collation is the
default for the new column type. 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.
When this form is used, the column's statistics are removed, so
running ANALYZE on the table afterwards is recommended.
SET/DROP DEFAULT
These forms set or remove the default value for a column (where
removal is equivalent to setting the default value to NULL). The
new default value will only apply in subsequent INSERT or UPDATE
commands; it does not cause rows already in the table to change.
SET/DROP NOT NULL
These forms change whether a column is marked to allow null values
or to reject null values.
SET NOT NULL may only be applied to a column provided none of the
records in the table contain a NULL value for the column.
Ordinarily this is checked during the ALTER TABLE by scanning the
entire table; however, if a valid CHECK constraint is found which
proves no NULL can exist, then the table scan is skipped.
If this table is a partition, one cannot perform DROP NOT NULL on a
column if it is marked NOT NULL in the parent table. To drop the
NOT NULL constraint from all the partitions, perform DROP NOT NULL
on the parent table. Even if there is no NOT NULL constraint on the
parent, such a constraint can still be added to individual
partitions, if desired; that is, the children can disallow nulls
even if the parent allows them, but not the other way around.
DROP EXPRESSION [ IF EXISTS ]
This form turns a stored generated column into a normal base
column. Existing data in the columns is retained, but future
changes will no longer apply the generation expression.
If DROP EXPRESSION IF EXISTS is specified and the column is not a
stored generated column, no error is thrown. In this case a notice
is issued instead.
ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY
SET GENERATED { ALWAYS | BY DEFAULT }
DROP IDENTITY [ IF EXISTS ]
These forms change whether a column is an identity column or change
the generation attribute of an existing identity column. See CREATE
TABLE for details. Like SET DEFAULT, these forms only affect the
behavior of subsequent INSERT and UPDATE commands; they do not
cause rows already in the table to change.
If DROP IDENTITY IF EXISTS is specified and the column is not an
identity column, no error is thrown. In this case a notice is
issued instead.
SET sequence_option
RESTART
These forms alter the sequence that underlies an existing identity
column. sequence_option is an option supported by ALTER SEQUENCE
such as INCREMENT BY.
SET STATISTICS
This form sets the per-column statistics-gathering target for
subsequent ANALYZE operations. The target can be set in the range 0
to 10000; 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 Section 14.2.
SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock.
SET ( attribute_option = value [, ... ] )
RESET ( attribute_option [, ... ] )
This form sets or resets per-attribute options. Currently, the only
defined per-attribute options are n_distinct and
n_distinct_inherited, which override the number-of-distinct-values
estimates made by subsequent ANALYZE operations. n_distinct
affects the statistics for the table itself, while
n_distinct_inherited affects the statistics gathered for the table
plus its inheritance children. When set to a positive value,
ANALYZE will assume that the column contains exactly the specified
number of distinct nonnull values. When set to a negative value,
which must be greater than or equal to -1, ANALYZE will assume that
the number of distinct nonnull values in the column is linear in
the size of the table; the exact count is to be computed by
multiplying the estimated table size by the absolute value of the
given number. For example, a value of -1 implies that all values in
the column are distinct, while a value of -0.5 implies that each
value appears twice on the average. This can be useful when the
size of the table changes over time, since the multiplication by
the number of rows in the table is not performed until query
planning time. Specify a value of 0 to revert to estimating the
number of distinct values normally. For more information on the use
of statistics by the PostgreSQL query planner, refer to
Section 14.2.
Changing per-attribute options acquires a SHARE UPDATE EXCLUSIVE
lock.
SET STORAGE
This form sets the storage mode for a column. This controls whether
this column is held inline or in a secondary TOAST 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 very large text and bytea values run 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 Section 73.2 for more
information.
SET COMPRESSION compression_method
This form sets the compression method for a column, determining how
values inserted in future will be compressed (if the storage mode
permits compression at all). This does not cause the table to be
rewritten, so existing data may still be compressed with other
compression methods. If the table is restored with pg_restore, then
all values are rewritten with the configured compression method.
However, when data is inserted from another relation (for example,
by INSERT ... SELECT), values from the source table are not
necessarily detoasted, so any previously compressed data may retain
its existing compression method, rather than being recompressed
with the compression method of the target column. The supported
compression methods are pglz and lz4. (lz4 is available only if
--with-lz4 was used when building PostgreSQL.) In addition,
compression_method can be default, which selects the default
behavior of consulting the default_toast_compression setting at the
time of data insertion to determine the method to use.
ADD table_constraint [ NOT VALID ]
This form adds a new constraint to a table using the same
constraint syntax as CREATE TABLE, plus the option NOT VALID, which
is currently only allowed for foreign key and CHECK constraints.
Normally, this form will cause a scan of the table to verify that
all existing rows in the table satisfy the new constraint. But if
the NOT VALID option is used, this potentially-lengthy scan is
skipped. The constraint will still be enforced against subsequent
inserts or updates (that is, they'll fail unless there is a
matching row in the referenced table, in the case of foreign keys,
or they'll fail unless the new row matches the specified check
condition). But the database will not assume that the constraint
holds for all rows in the table, until it is validated by using the
VALIDATE CONSTRAINT option. See Notes below for more information
about using the NOT VALID option.
Although most forms of ADD table_constraint require an ACCESS
EXCLUSIVE lock, ADD FOREIGN KEY requires only a SHARE ROW EXCLUSIVE
lock. Note that ADD FOREIGN KEY also acquires a SHARE ROW EXCLUSIVE
lock on the referenced table, in addition to the lock on the table
on which the constraint is declared.
Additional restrictions apply when unique or primary key
constraints are added to partitioned tables; see CREATE TABLE.
Also, foreign key constraints on partitioned tables may not be
declared NOT VALID at present.
ADD table_constraint_using_index
This form adds a new PRIMARY KEY or UNIQUE constraint to a table
based on an existing unique index. All the columns of the index
will be included in the constraint.
The index cannot have expression columns nor be a partial index.
Also, it must be a b-tree index with default sort ordering. These
restrictions ensure that the index is equivalent to one that would
be built by a regular ADD PRIMARY KEY or ADD UNIQUE command.
If PRIMARY KEY is specified, and the index's columns are not
already marked NOT NULL, then this command will attempt to do ALTER
COLUMN SET NOT NULL against each such column. That requires a full
table scan to verify the column(s) contain no nulls. In all other
cases, this is a fast operation.
If a constraint name is provided then the index will be renamed to
match the constraint name. Otherwise the constraint will be named
the same as the index.
After this command is executed, the index is “owned” by the
constraint, in the same way as if the index had been built by a
regular ADD PRIMARY KEY or ADD UNIQUE command. In particular,
dropping the constraint will make the index disappear too.
This form is not currently supported on partitioned tables.
Note
Adding a constraint using an existing index can be helpful in
situations where a new constraint needs to be added without
blocking table updates for a long time. To do that, create the
index using CREATE INDEX CONCURRENTLY, and then install it as
an official constraint using this syntax. See the example
below.
ALTER CONSTRAINT
This form alters the attributes of a constraint that was previously
created. Currently only foreign key constraints may be altered.
VALIDATE CONSTRAINT
This form validates a foreign key or check constraint that was
previously created as NOT VALID, by scanning the table to ensure
there are no rows for which the constraint is not satisfied.
Nothing happens if the constraint is already marked valid. (See
Notes below for an explanation of the usefulness of this command.)
This command acquires a SHARE UPDATE EXCLUSIVE lock.
DROP CONSTRAINT [ IF EXISTS ]
This form drops the specified constraint on a table, along with any
index underlying the constraint. If IF EXISTS is specified and the
constraint does not exist, no error is thrown. In this case a
notice is issued instead.
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 internally generated
constraint triggers, such as those that are used to implement
foreign key constraints or deferrable uniqueness and exclusion
constraints). Disabling or enabling internally generated 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 (the
default) will fire when the replication role is “origin” (the
default) or “local”. Triggers configured as ENABLE REPLICA will
only fire if the session is in “replica” mode, and triggers
configured as ENABLE ALWAYS will fire regardless of the current
replication role.
The effect of this mechanism is that in the default configuration,
triggers do not fire on replicas. This is useful because if a
trigger is used on the origin to propagate data between tables,
then the replication system will also replicate the propagated
data; so the trigger should not fire a second time on the replica,
because that would lead to duplication. However, if a trigger is
used for another purpose such as creating external alerts, then it
might be appropriate to set it to ENABLE ALWAYS so that it is also
fired on replicas.
When this command is applied to a partitioned table, the states of
corresponding clone triggers in the partitions are updated too,
unless ONLY is specified.
This command acquires a SHARE ROW EXCLUSIVE lock.
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 configuration 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 replication
role.
The rule firing mechanism is also affected by the configuration
variable session_replication_role, analogous to triggers as
described above.
DISABLE/ENABLE ROW LEVEL SECURITY
These forms control the application of row security policies
belonging to the table. If enabled and no policies exist for the
table, then a default-deny policy is applied. Note that policies
can exist for a table even if row-level security is disabled. In
this case, the policies will not be applied and the policies will
be ignored. See also CREATE POLICY.
NO FORCE/FORCE ROW LEVEL SECURITY
These forms control the application of row security policies
belonging to the table when the user is the table owner. If
enabled, row-level security policies will be applied when the user
is the table owner. If disabled (the default) then row-level
security will not be applied when the user is the table owner. See
also CREATE POLICY.
CLUSTER ON
This form selects the default index for future CLUSTER operations.
It does not actually re-cluster the table.
Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock.
SET WITHOUT CLUSTER
This form removes the most recently used CLUSTER index
specification from the table. This affects future cluster
operations that don't specify an index.
Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock.
SET WITHOUT OIDS
Backward-compatible syntax for removing the oid system column. As
oid system columns cannot be added anymore, this never has an
effect.
SET ACCESS METHOD
This form changes the access method of the table by rewriting it.
See Chapter 63 for more information.
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. When applied to a partitioned table, nothing is moved,
but any partitions created afterwards with CREATE TABLE PARTITION
OF will use that tablespace, unless overridden by a TABLESPACE
clause.
All tables in the current database in a tablespace can be moved by
using the ALL IN TABLESPACE form, which will lock all tables to be
moved first and then move each one. This form also supports OWNED
BY, which will only move tables owned by the roles specified. If
the NOWAIT option is specified then the command will fail if it is
unable to acquire all of the locks required immediately. Note that
system catalogs are not moved by this command; use ALTER DATABASE
or explicit ALTER TABLE invocations instead if desired. The
information_schema relations are not considered part of the system
catalogs and will be moved. See also CREATE TABLESPACE.
SET { LOGGED | UNLOGGED }
This form changes the table from unlogged to logged or vice-versa
(see UNLOGGED). It cannot be applied to a temporary table.
This also changes the persistence of any sequences linked to the
table (for identity or serial columns). However, it is also
possible to change the persistence of such sequences separately.
SET ( storage_parameter [= value] [, ... ] )
This form changes one or more storage parameters for the table. See
Storage Parameters in the CREATE TABLE documentation for details on
the available parameters. Note that the table contents will not be
modified immediately by this command; depending on the parameter
you might need to rewrite the table to get the desired effects.
That can be done with VACUUM FULL, CLUSTER or one of the forms of
ALTER TABLE that forces a table rewrite. For planner related
parameters, changes will take effect from the next time the table
is locked so currently executing queries will not be affected.
SHARE UPDATE EXCLUSIVE lock will be taken for fillfactor, toast and
autovacuum storage parameters, as well as the planner parameter
parallel_workers.
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 table. 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 constraints 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
constraints of the parent, except those marked non-inheritable
(that is, created with ALTER TABLE ... ADD CONSTRAINT ... NO
INHERIT) in the parent, which are ignored; all child-table
constraints matched must not be marked non-inheritable. Currently
UNIQUE, PRIMARY KEY, and FOREIGN KEY constraints 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
specified parent table. Queries against the parent table will no
longer include records drawn from the target table.
OF type_name
This form links the table to a composite type as though CREATE
TABLE OF had formed it. The table's list of column names and types
must precisely match that of the composite type. The table must not
inherit from any other table. These restrictions ensure that CREATE
TABLE OF would permit an equivalent table definition.
NOT OF
This form dissociates a typed table from its type.
OWNER TO
This form changes the owner of the table, sequence, view,
materialized view, or foreign table to the specified user.
REPLICA IDENTITY
This form changes the information which is written to the
write-ahead log to identify rows which are updated or deleted. In
most cases, the old value of each column is only logged if it
differs from the new value; however, if the old value is stored
externally, it is always logged regardless of whether it changed.
This option has no effect except when logical replication is in
use.
DEFAULT
Records the old values of the columns of the primary key, if
any. This is the default for non-system tables.
USING INDEX index_name
Records the old values of the columns covered by the named
index, that must be unique, not partial, not deferrable, and
include only columns marked NOT NULL. If this index is dropped,
the behavior is the same as NOTHING.
FULL
Records the old values of all columns in the row.
NOTHING
Records no information about the old row. This is the default
for system tables.
RENAME
The RENAME forms change the name of a table (or an index, sequence,
view, materialized view, or foreign table), the name of an
individual column in a table, or the name of a constraint of the
table. When renaming a constraint that has an underlying index, the
index is renamed as well. There is no effect on the stored data.
SET SCHEMA
This form moves the table into another schema. Associated indexes,
constraints, and sequences owned by table columns are moved as
well.
ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec |
DEFAULT }
This form attaches an existing table (which might itself be
partitioned) as a partition of the target table. The table can be
attached as a partition for specific values using FOR VALUES or as
a default partition by using DEFAULT. For each index in the target
table, a corresponding one will be created in the attached table;
or, if an equivalent index already exists, it will be attached to
the target table's index, as if ALTER INDEX ATTACH PARTITION had
been executed. Note that if the existing table is a foreign table,
it is currently not allowed to attach the table as a partition of
the target table if there are UNIQUE indexes on the target table.
(See also CREATE FOREIGN TABLE (CREATE_FOREIGN_TABLE(7)).) For each
user-defined row-level trigger that exists in the target table, a
corresponding one is created in the attached table.
A partition using FOR VALUES uses same syntax for
partition_bound_spec as CREATE TABLE. The partition bound
specification must correspond to the partitioning strategy and
partition key of the target table. The table to be attached must
have all the same columns as the target table and no more;
moreover, the column types must also match. Also, it must have all
the NOT NULL and CHECK constraints of the target table. Currently
FOREIGN KEY constraints are not considered. UNIQUE and PRIMARY KEY
constraints from the parent table will be created in the partition,
if they don't already exist. If any of the CHECK constraints of the
table being attached are marked NO INHERIT, the command will fail;
such constraints must be recreated without the NO INHERIT clause.
If the new partition is a regular table, a full table scan is
performed to check that existing rows in the table do not violate
the partition constraint. It is possible to avoid this scan by
adding a valid CHECK constraint to the table that allows only rows
satisfying the desired partition constraint before running this
command. The CHECK constraint will be used to determine that the
table need not be scanned to validate the partition constraint.
This does not work, however, if any of the partition keys is an
expression and the partition does not accept NULL values. If
attaching a list partition that will not accept NULL values, also
add a NOT NULL constraint to the partition key column, unless it's
an expression.
If the new partition is a foreign table, nothing is done to verify
that all the rows in the foreign table obey the partition
constraint. (See the discussion in CREATE FOREIGN TABLE
(CREATE_FOREIGN_TABLE(7)) about constraints on the foreign table.)
When a table has a default partition, defining a new partition
changes the partition constraint for the default partition. The
default partition can't contain any rows that would need to be
moved to the new partition, and will be scanned to verify that none
are present. This scan, like the scan of the new partition, can be
avoided if an appropriate CHECK constraint is present. Also like
the scan of the new partition, it is always skipped when the
default partition is a foreign table.
Attaching a partition acquires a SHARE UPDATE EXCLUSIVE lock on the
parent table, in addition to the ACCESS EXCLUSIVE locks on the
table being attached and on the default partition (if any).
Further locks must also be held on all sub-partitions if the table
being attached is itself a partitioned table. Likewise if the
default partition is itself a partitioned table. The locking of the
sub-partitions can be avoided by adding a CHECK constraint as
described in Section 5.11.2.2.
DETACH PARTITION partition_name [ CONCURRENTLY | FINALIZE ]
This form detaches the specified partition of the target table. The
detached partition continues to exist as a standalone table, but no
longer has any ties to the table from which it was detached. Any
indexes that were attached to the target table's indexes are
detached. Any triggers that were created as clones of those in the
target table are removed. SHARE lock is obtained on any tables
that reference this partitioned table in foreign key constraints.
If CONCURRENTLY is specified, it runs using a reduced lock level to
avoid blocking other sessions that might be accessing the
partitioned table. In this mode, two transactions are used
internally. During the first transaction, a SHARE UPDATE EXCLUSIVE
lock is taken on both parent table and partition, and the partition
is marked as undergoing detach; at that point, the transaction is
committed and all other transactions using the partitioned table
are waited for. Once all those transactions have completed, the
second transaction acquires SHARE UPDATE EXCLUSIVE on the
partitioned table and ACCESS EXCLUSIVE on the partition, and the
detach process completes. A CHECK constraint that duplicates the
partition constraint is added to the partition. CONCURRENTLY
cannot be run in a transaction block and is not allowed if the
partitioned table contains a default partition.
If FINALIZE is specified, a previous DETACH CONCURRENTLY invocation
that was canceled or interrupted is completed. At most one
partition in a partitioned table can be pending detach at a time.
All the forms of ALTER TABLE that act on a single table, except RENAME,
SET SCHEMA, ATTACH PARTITION, and DETACH PARTITION can be combined into
a list of multiple alterations to be applied together. 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 or
tablespace of a table, you must also have CREATE privilege on the new
schema or tablespace. To add the table as a new child of a parent
table, you must own the parent table as well. Also, to attach a table
as a new partition of the table, you must own the table being attached.
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.)
To add a column or alter a column type or use the OF clause, you must
also have USAGE privilege on the data type.
PARAMETERS
IF EXISTS
Do not throw an error if the table does not exist. A notice is
issued in this case.
name
The name (optionally schema-qualified) of an existing table to
alter. If ONLY is specified before the table name, only that table
is altered. If ONLY is not specified, the table and all its
descendant tables (if any) are altered. Optionally, * can be
specified after the table name to explicitly indicate that
descendant tables are included.
column_name
Name of a new or existing column.
new_column_name
New name for an existing column.
new_name
New name for the table.
data_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 a new or existing constraint.
CASCADE
Automatically drop objects that depend on the dropped column or
constraint (for example, views referencing the column), and in turn
all objects that depend on those objects (see Section 5.14).
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 superuser privilege if any of the triggers are internally
generated constraint triggers, such as those that are used to
implement foreign key constraints or deferrable uniqueness and
exclusion constraints.)
USER
Disable or enable all triggers belonging to the table except for
internally generated constraint triggers, such as those that are
used to implement foreign key constraints or deferrable uniqueness
and exclusion constraints.
index_name
The name of an existing index.
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_access_method
The name of the access method to which the table will be converted.
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.
partition_name
The name of the table to attach as a new partition or to detach
from this table.
partition_bound_spec
The partition bound specification for a new partition. Refer to
CREATE TABLE (CREATE_TABLE(7)) for more details on the syntax of
the same.
NOTES
The key word COLUMN is noise and can be omitted.
When a column is added with ADD COLUMN and a non-volatile DEFAULT is
specified, the default is evaluated at the time of the statement and
the result stored in the table's metadata. That value will be used for
the column for all existing rows. If no DEFAULT is specified, NULL is
used. In neither case is a rewrite of the table required.
Adding a column with a volatile DEFAULT or changing the type of an
existing column will require the entire table and its indexes to be
rewritten. As an exception, when changing the type of an existing
column, if the USING clause does not change the column contents and the
old type is either binary coercible to the new type or an unconstrained
domain over the new type, a table rewrite is not needed. However,
indexes must always be rebuilt unless the system can verify that the
new index would be logically equivalent to the existing one. For
example, if the collation for a column has been changed, an index
rebuild is always required because the new sort order might be
different. However, in the absence of a collation change, a column can
be changed from text to varchar (or vice versa) without rebuilding the
indexes because these data types sort identically. Table and/or index
rebuilds may take a significant amount of time for a large table; and
will temporarily require as much as double the disk space.
Adding a CHECK or NOT NULL constraint requires scanning the table to
verify that existing rows meet the constraint, but does not require a
table rewrite.
Similarly, when attaching a new partition it may be scanned to verify
that existing rows meet the partition 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.
Scanning a large table to verify a new foreign key or check constraint
can take a long time, and other updates to the table are locked out
until the ALTER TABLE ADD CONSTRAINT command is committed. The main
purpose of the NOT VALID constraint option is to reduce the impact of
adding a constraint on concurrent updates. With NOT VALID, the ADD
CONSTRAINT command does not scan the table and can be committed
immediately. After that, a VALIDATE CONSTRAINT command can be issued to
verify that existing rows satisfy the constraint. The validation step
does not need to lock out concurrent updates, since it knows that other
transactions will be enforcing the constraint for rows that they insert
or update; only pre-existing rows need to be checked. Hence, validation
acquires only a SHARE UPDATE EXCLUSIVE lock on the table being altered.
(If the constraint is a foreign key then a ROW SHARE lock is also
required on the table referenced by the constraint.) In addition to
improving concurrency, it can be useful to use NOT VALID and VALIDATE
CONSTRAINT in cases where the table is known to contain pre-existing
violations. Once the constraint is in place, no new violations can be
inserted, and the existing problems can be corrected at leisure until
VALIDATE CONSTRAINT finally succeeds.
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.
To force immediate reclamation of space occupied by a dropped column,
you can execute one of the forms of ALTER TABLE that performs a rewrite
of the whole table. This results in reconstructing each row with the
dropped column replaced by a null value.
The rewriting forms of ALTER TABLE are not MVCC-safe. After a table
rewrite, the table will appear empty to concurrent transactions, if
they are using a snapshot taken before the rewrite occurred. See
Section 13.6 for more details.
The USING option of SET DATA 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 SET DATA 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, SET DATA TYPE might 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. This ensures that the descendants
always have columns matching the parent. Similarly, a CHECK constraint
cannot be renamed in the parent without also renaming it in all
descendants, so that CHECK constraints also match between the parent
and its descendants. (That restriction does not apply to index-based
constraints, however.) Also, because selecting from the parent also
selects from its descendants, a constraint on the parent cannot be
marked valid unless it is also marked valid for those descendants. In
all of these cases, ALTER TABLE ONLY will be rejected.
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. A nonrecursive DROP COLUMN command will
fail for a partitioned table, because all partitions of a table must
have the same columns as the partitioning root.
The actions for identity columns (ADD GENERATED, SET etc., DROP
IDENTITY), as well as the actions CLUSTER, OWNER, and TABLESPACE never
recurse to descendant tables; that is, they always act as though ONLY
were specified. Actions affecting trigger states recurse to partitions
of partitioned tables (unless ONLY is specified), but never to
traditional-inheritance descendants. Adding a constraint recurses only
for CHECK constraints that are not marked NO INHERIT.
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. Chapter 5 has further information on inheritance.
EXAMPLES
To add a column of type varchar to a table:
ALTER TABLE distributors ADD COLUMN address varchar(30);
That will cause all existing rows in the table to be filled with null
values for the new column.
To add a column with a non-null default:
ALTER TABLE measurements
ADD COLUMN mtime timestamp with time zone DEFAULT now();
Existing rows will be filled with the current time as the value of the
new column, and then new rows will receive the time of their insertion.
To add a column and fill it with a value different from the default to
be used later:
ALTER TABLE transactions
ADD COLUMN status varchar(30) DEFAULT 'old',
ALTER COLUMN status SET default 'current';
Existing rows will be filled with old, but then the default for
subsequent commands will be current. The effects are the same as if the
two sub-commands had been issued in separate ALTER TABLE commands.
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 SET DATA 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 rename an existing constraint:
ALTER TABLE distributors RENAME CONSTRAINT zipchk TO zip_check;
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 and all its children:
ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);
To add a check constraint only to a table and not to its children:
ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5) NO INHERIT;
(The check constraint will not be inherited by future children,
either.)
To remove a check constraint from a table and all its children:
ALTER TABLE distributors DROP CONSTRAINT zipchk;
To remove a check constraint from one table only:
ALTER TABLE ONLY distributors DROP CONSTRAINT zipchk;
(The check constraint remains in place for any child tables.)
To add a foreign key constraint to a table:
ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address);
To add a foreign key constraint to a table with the least impact on
other work:
ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) NOT VALID;
ALTER TABLE distributors VALIDATE CONSTRAINT distfk;
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;
To recreate a primary key constraint, without blocking updates while
the index is rebuilt:
CREATE UNIQUE INDEX CONCURRENTLY dist_id_temp_idx ON distributors (dist_id);
ALTER TABLE distributors DROP CONSTRAINT distributors_pkey,
ADD CONSTRAINT distributors_pkey PRIMARY KEY USING INDEX dist_id_temp_idx;
To attach a partition to a range-partitioned table:
ALTER TABLE measurement
ATTACH PARTITION measurement_y2016m07 FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');
To attach a partition to a list-partitioned table:
ALTER TABLE cities
ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');
To attach a partition to a hash-partitioned table:
ALTER TABLE orders
ATTACH PARTITION orders_p4 FOR VALUES WITH (MODULUS 4, REMAINDER 3);
To attach a default partition to a partitioned table:
ALTER TABLE cities
ATTACH PARTITION cities_partdef DEFAULT;
To detach a partition from a partitioned table:
ALTER TABLE measurement
DETACH PARTITION measurement_y2015m12;
COMPATIBILITY
The forms ADD (without USING INDEX), DROP [COLUMN], DROP IDENTITY,
RESTART, SET DEFAULT, SET DATA TYPE (without USING), SET GENERATED, and
SET sequence_option 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.
SEE ALSO
CREATE TABLE (CREATE_TABLE(7))
PostgreSQL 15.7 2024 ALTER TABLE(7)
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