ALTER TABLE — change the definition of a table
ALTER TABLE [ IF EXISTS ] [ ONLY ]name
[ * ]action
[, ... ] ALTER TABLE [ IF EXISTS ] [ ONLY ]name
[ * ] RENAME [ COLUMN ]column_name
TOnew_column_name
ALTER TABLE [ IF EXISTS ] [ ONLY ]name
[ * ] RENAME CONSTRAINTconstraint_name
TOnew_constraint_name
ALTER TABLE [ IF EXISTS ]name
RENAME TOnew_name
ALTER TABLE [ IF EXISTS ]name
SET SCHEMAnew_schema
ALTER TABLE ALL IN TABLESPACEname
[ OWNED BYrole_name
[, ... ] ] SET TABLESPACEnew_tablespace
[ NOWAIT ] ALTER TABLE [ IF EXISTS ]name
ATTACH PARTITIONpartition_name
{ FOR VALUESpartition_bound_spec
| DEFAULT } ALTER TABLE [ IF EXISTS ]name
DETACH PARTITIONpartition_name
[ CONCURRENTLY | FINALIZE ] whereaction
is one of: ADD [ COLUMN ] [ IF NOT EXISTS ]column_name
data_type
[ COLLATEcollation
] [column_constraint
[ ... ] ] DROP [ COLUMN ] [ IF EXISTS ]column_name
[ RESTRICT | CASCADE ] ALTER [ COLUMN ]column_name
[ SET DATA ] TYPEdata_type
[ COLLATEcollation
] [ USINGexpression
] ALTER [ COLUMN ]column_name
SET DEFAULTexpression
ALTER [ COLUMN ]column_name
DROP DEFAULT ALTER [ COLUMN ]column_name
SET MASKexpression
ALTER [ COLUMN ]column_name
DROP MASK ALTER [ COLUMN ]column_name
{ SET | DROP } NOT NULL ALTER [ COLUMN ]column_name
SET EXPRESSION AS (expression
) 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 } | SETsequence_option
| RESTART [ [ WITH ]restart
] } [...] ALTER [ COLUMN ]column_name
DROP IDENTITY [ IF EXISTS ] ALTER [ COLUMN ]column_name
SET STATISTICS {integer
| DEFAULT } 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 | DEFAULT } ALTER [ COLUMN ]column_name
SET COMPRESSIONcompression_method
ADDtable_constraint
[ NOT VALID ] ADDtable_constraint_using_index
ALTER CONSTRAINTconstraint_name
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] VALIDATE CONSTRAINTconstraint_name
DROP CONSTRAINT [ IF EXISTS ]constraint_name
[ RESTRICT | CASCADE ] DISABLE TRIGGER [trigger_name
| ALL | USER ] ENABLE TRIGGER [trigger_name
| ALL | USER ] ENABLE REPLICA TRIGGERtrigger_name
ENABLE ALWAYS TRIGGERtrigger_name
DISABLE RULErewrite_rule_name
ENABLE RULErewrite_rule_name
ENABLE REPLICA RULErewrite_rule_name
ENABLE ALWAYS RULErewrite_rule_name
DISABLE ROW LEVEL SECURITY ENABLE ROW LEVEL SECURITY FORCE ROW LEVEL SECURITY NO FORCE ROW LEVEL SECURITY CLUSTER ONindex_name
SET WITHOUT CLUSTER SET WITHOUT OIDS SET ACCESS METHOD {new_access_method
| DEFAULT } SET TABLESPACEnew_tablespace
SET { LOGGED | UNLOGGED } SET (storage_parameter
[=value
] [, ... ] ) RESET (storage_parameter
[, ... ] ) INHERITparent_table
NO INHERITparent_table
OFtype_name
NOT OF OWNER TO {new_owner
| CURRENT_ROLE | CURRENT_USER | SESSION_USER } REPLICA IDENTITY { DEFAULT | USING INDEXindex_name
| FULL | NOTHING } andpartition_bound_spec
is: IN (partition_bound_expr
[, ...] ) | FROM ( {partition_bound_expr
| MINVALUE | MAXVALUE } [, ...] ) TO ( {partition_bound_expr
| MINVALUE | MAXVALUE } [, ...] ) | WITH ( MODULUSnumeric_literal
, REMAINDERnumeric_literal
) andcolumn_constraint
is: [ CONSTRAINTconstraint_name
] { NOT NULL | NULL | CHECK (expression
) [ NO INHERIT ] | DEFAULTdefault_expr
| GENERATED ALWAYS AS (generation_expr
) STORED | GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ (sequence_options
) ] | UNIQUE [ NULLS [ NOT ] DISTINCT ]index_parameters
| PRIMARY KEYindex_parameters
| REFERENCESreftable
[ (refcolumn
) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETEreferential_action
] [ ON UPDATEreferential_action
] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] andtable_constraint
is: [ CONSTRAINTconstraint_name
] { CHECK (expression
) [ NO INHERIT ] | UNIQUE [ NULLS [ NOT ] DISTINCT ] (column_name
[, ... ] )index_parameters
| PRIMARY KEY (column_name
[, ... ] )index_parameters
| EXCLUDE [ USINGindex_method
] (exclude_element
WITHoperator
[, ... ] )index_parameters
[ WHERE (predicate
) ] | FOREIGN KEY (column_name
[, ... ] ) REFERENCESreftable
[ (refcolumn
[, ... ] ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETEreferential_action
] [ ON UPDATEreferential_action
] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] andtable_constraint_using_index
is: [ CONSTRAINTconstraint_name
] { UNIQUE | PRIMARY KEY } USING INDEXindex_name
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]index_parameters
inUNIQUE
,PRIMARY KEY
, andEXCLUDE
constraints are: [ INCLUDE (column_name
[, ... ] ) ] [ WITH (storage_parameter
[=value
] [, ... ] ) ] [ USING INDEX TABLESPACEtablespace_name
]exclude_element
in anEXCLUDE
constraint is: {column_name
| (expression
) } [ COLLATEcollation
] [opclass
[ (opclass_parameter
=value
[, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]referential_action
in aFOREIGN KEY
/REFERENCES
constraint is: { NO ACTION | RESTRICT | CASCADE | SET NULL [ (column_name
[, ... ] ) ] | SET DEFAULT [ (column_name
[, ... ] ) ] }
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 MASK
#
These forms set or remove the masking expression for a column. The
expression does not affect what the INSERT
or UPDATE
commands will store in the column. Rather,
the expression only determines the value received by
pg_dump or
by logical replication
subscribtion.
The masking expression can refer to other columns in the table. It cannot contain user-defined functions, operators, types, and collations, system column references or non-immutable built-in functions. The expression value must be of the same data type as the column it's defined on.
Masking expression cannot be defined on an expression-generated column
(that is, a column having the GENERATED ALWAYS AS
... STORED
constraint).
Note that the masking expressions of table partitions are controlled by
the root table. An attempt to set the expression on a partition will
result in error. The ATTACH PARTITION
subcommand will
set the masking expressions of the new partition according to the target
(partitioned) table. Likewise, the masking expressions of a child table
are controlled by the parent table. The INHERIT
subcommand will set the masking expression of the new child table
according to the parent table.
See Chapter 32 for more information on how the masking expressions can be used.
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.
SET EXPRESSION AS
#This form replaces the expression of a generated column. Existing data in the column is rewritten and all the future changes will apply the new generation expression.
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. Set it
to DEFAULT
to revert to using the system default
statistics target (default_statistics_target).
(Setting to a value of -1 is an obsolete way spelling to get the same
outcome.)
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 { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
#
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.
Writing DEFAULT
sets the storage mode to the default
mode for the column's data type. 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 ALTER TABLE ... SET STORAGE
doesn't itself
change anything in the table; it just sets the strategy to be pursued
during future table updates.
See Section 67.2 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
require an table_constraint
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.
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 UNIQUE INDEX CONCURRENTLY
, and then convert it to a
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
using the indicated access method; specifying
DEFAULT
selects the access method set as the
default_table_access_method configuration
parameter.
See Chapter 63 for more information.
When applied to a partitioned table, there is no data to rewrite,
but partitions created afterwards will default to the given access
method unless overridden by a USING
clause.
Specifying DEFAULT
removes a previous value,
causing future partitions to default to
default_table_access_method
.
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.) 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, not marked
NO INHERIT
. 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 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 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 5.12.2.2.
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 be able to SET ROLE
to 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.
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 5.15).
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 for more details on the syntax of the same.
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 for a further description of valid parameters. Chapter 5 has further information on inheritance.
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;
The forms ADD
(without USING INDEX
),
DROP [COLUMN]
, DROP IDENTITY
, RESTART
,
SET DEFAULT
, SET DATA TYPE
(without USING
),
SET GENERATED
, and SET
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
sequence_option
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.