NAME
ALTER_TABLE - change the definition of a table
SYNOPSIS
ALTER TABLE [ IF EXISTS ] [ ONLY ] \nname\n [ * ]
\n
\naction\n [, ... ]
ALTER TABLE [ IF EXISTS ] [ ONLY ] \nname\n [ * ]
\n
RENAME [ COLUMN ] \ncolumn_name\n TO \nnew_column_name\n
ALTER TABLE [ IF EXISTS ] [ ONLY ] \nname\n [ * ]
\n
RENAME CONSTRAINT \nconstraint_name\n TO \nnew_constraint_name\n
ALTER TABLE [ IF EXISTS ] \nname\n
\n
RENAME TO \nnew_name\n
ALTER TABLE [ IF EXISTS ] \nname\n
\n
SET SCHEMA \nnew_schema\n
ALTER TABLE ALL IN TABLESPACE \nname\n [ OWNED BY \nrole_name\n [, ... ] ]
\n
SET TABLESPACE \nnew_tablespace\n [ NOWAIT ]
ALTER TABLE [ IF EXISTS ] \nname\n
\n
ATTACH PARTITION \npartition_name\n { FOR VALUES \npartition_bound_spec\n | DEFAULT }
ALTER TABLE [ IF EXISTS ] \nname\n
\n
DETACH PARTITION \npartition_name\n [ CONCURRENTLY | FINALIZE ]
where \naction\n is one of:
\n
ADD [ COLUMN ] [ IF NOT EXISTS ] \ncolumn_name\n \ndata_type\n [ COLLATE \ncollation\n ] [ \ncolumn_constraint\n [ ... ] ]
\n
DROP [ COLUMN ] [ IF EXISTS ] \ncolumn_name\n [ RESTRICT | CASCADE ]
\n
ALTER [ COLUMN ] \ncolumn_name\n [ SET DATA ] TYPE \ndata_type\n [ COLLATE \ncollation\n ] [ USING \nexpression\n ]
\n
ALTER [ COLUMN ] \ncolumn_name\n SET DEFAULT \nexpression\n
\n
ALTER [ COLUMN ] \ncolumn_name\n DROP DEFAULT
\n
ALTER [ COLUMN ] \ncolumn_name\n { SET | DROP } NOT NULL
\n
ALTER [ COLUMN ] \ncolumn_name\n SET EXPRESSION AS ( \nexpression\n )
\n
ALTER [ COLUMN ] \ncolumn_name\n DROP EXPRESSION [ IF EXISTS ]
\n
ALTER [ COLUMN ] \ncolumn_name\n ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( \nsequence_options\n ) ]
\n
ALTER [ COLUMN ] \ncolumn_name\n { SET GENERATED { ALWAYS | BY DEFAULT } | SET \nsequence_option\n | RESTART [ [ WITH ] \nrestart\n ] } [...]
\n
ALTER [ COLUMN ] \ncolumn_name\n DROP IDENTITY [ IF EXISTS ]
\n
ALTER [ COLUMN ] \ncolumn_name\n SET STATISTICS { \ninteger\n | DEFAULT }
\n
ALTER [ COLUMN ] \ncolumn_name\n SET ( \nattribute_option\n = \nvalue\n [, ... ] )
\n
ALTER [ COLUMN ] \ncolumn_name\n RESET ( \nattribute_option\n [, ... ] )
\n
ALTER [ COLUMN ] \ncolumn_name\n SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
\n
ALTER [ COLUMN ] \ncolumn_name\n SET COMPRESSION \ncompression_method\n
\n
ADD \ntable_constraint\n [ NOT VALID ]
\n
ADD \ntable_constraint_using_index\n
\n
ALTER CONSTRAINT \nconstraint_name\n [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
\n
VALIDATE CONSTRAINT \nconstraint_name\n
\n
DROP CONSTRAINT [ IF EXISTS ] \nconstraint_name\n [ RESTRICT | CASCADE ]
\n
DISABLE TRIGGER [ \ntrigger_name\n | ALL | USER ]
\n
ENABLE TRIGGER [ \ntrigger_name\n | ALL | USER ]
\n
ENABLE REPLICA TRIGGER \ntrigger_name\n
\n
ENABLE ALWAYS TRIGGER \ntrigger_name\n
\n
DISABLE RULE \nrewrite_rule_name\n
\n
ENABLE RULE \nrewrite_rule_name\n
\n
ENABLE REPLICA RULE \nrewrite_rule_name\n
\n
ENABLE ALWAYS RULE \nrewrite_rule_name\n
\n
DISABLE ROW LEVEL SECURITY
\n
ENABLE ROW LEVEL SECURITY
\n
FORCE ROW LEVEL SECURITY
\n
NO FORCE ROW LEVEL SECURITY
\n
CLUSTER ON \nindex_name\n
\n
SET WITHOUT CLUSTER
\n
SET WITHOUT OIDS
\n
SET ACCESS METHOD { \nnew_access_method\n | DEFAULT }
\n
SET TABLESPACE \nnew_tablespace\n
\n
SET { LOGGED | UNLOGGED }
\n
SET ( \nstorage_parameter\n [= \nvalue\n] [, ... ] )
\n
RESET ( \nstorage_parameter\n [, ... ] )
\n
INHERIT \nparent_table\n
\n
NO INHERIT \nparent_table\n
\n
OF \ntype_name\n
\n
NOT OF
\n
OWNER TO { \nnew_owner\n | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
\n
REPLICA IDENTITY { DEFAULT | USING INDEX \nindex_name\n | FULL | NOTHING }
and \npartition_bound_spec\n is:
IN ( \npartition_bound_expr\n [, ...] ) |
FROM ( { \npartition_bound_expr\n | MINVALUE | MAXVALUE } [, ...] )
\n
TO ( { \npartition_bound_expr\n | MINVALUE | MAXVALUE } [, ...] ) |
WITH ( MODULUS \nnumeric_literal\n, REMAINDER \nnumeric_literal\n )
and \ncolumn_constraint\n is:
[ CONSTRAINT \nconstraint_name\n ]
{ NOT NULL |
\n
NULL |
\n
CHECK ( \nexpression\n ) [ NO INHERIT ] |
\n
DEFAULT \ndefault_expr\n |
\n
GENERATED ALWAYS AS ( \ngeneration_expr\n ) STORED |
\n
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( \nsequence_options\n ) ] |
\n
UNIQUE [ NULLS [ NOT ] DISTINCT ] \nindex_parameters\n |
\n
PRIMARY KEY \nindex_parameters\n |
\n
REFERENCES \nreftable\n [ ( \nrefcolumn\n ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
\n
[ ON DELETE \nreferential_action\n ] [ ON UPDATE \nreferential_action\n ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and \ntable_constraint\n is:
[ CONSTRAINT \nconstraint_name\n ]
{ CHECK ( \nexpression\n ) [ NO INHERIT ] |
\n
UNIQUE [ NULLS [ NOT ] DISTINCT ] ( \ncolumn_name\n [, ... ] ) \nindex_parameters\n |
\n
PRIMARY KEY ( \ncolumn_name\n [, ... ] ) \nindex_parameters\n |
\n
EXCLUDE [ USING \nindex_method\n ] ( \nexclude_element\n WITH \noperator\n [, ... ] ) \nindex_parameters\n [ WHERE ( \npredicate\n ) ] |
\n
FOREIGN KEY ( \ncolumn_name\n [, ... ] ) REFERENCES \nreftable\n [ ( \nrefcolumn\n [, ... ] ) ]
\n
[ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE \nreferential_action\n ] [ ON UPDATE \nreferential_action\n ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and \ntable_constraint_using_index\n is:
\n
[ CONSTRAINT \nconstraint_name\n ]
\n
{ UNIQUE | PRIMARY KEY } USING INDEX \nindex_name\n
\n
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
\nindex_parameters\n in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are:
[ INCLUDE ( \ncolumn_name\n [, ... ] ) ]
[ WITH ( \nstorage_parameter\n [= \nvalue\n] [, ... ] ) ]
[ USING INDEX TABLESPACE \ntablespace_name\n ]
\nexclude_element\n in an EXCLUDE constraint is:
{ \ncolumn_name\n | ( \nexpression\n ) } [ COLLATE \ncollation\n ] [ \nopclass\n [ ( \nopclass_parameter\n = \nvalue\n [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
\nreferential_action\n in a FOREIGN KEY/REFERENCES constraint is:
{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( \ncolumn_name\n [, ... ] ) ] | SET DEFAULT [ ( \ncolumn_name\n [, ... ] ) ] }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 ]
DROP COLUMN [ IF EXISTS ]
SET DATA TYPE
When this form is used, the column's statistics are removed, so running ANALYZE on the table afterwards is recommended.
SET/DROP DEFAULT
SET/DROP NOT NULL
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 exists (and is not dropped in the same command) 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
When this form is used, the column's statistics are removed, so running ANALYZE on the table afterwards is recommended.
DROP EXPRESSION [ IF EXISTS ]
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 ]
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
SET STATISTICS
SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock.
SET ( attribute_option = value [, ... ] ) RESET ( attribute_option [, ... ] )
Changing per-attribute options acquires a SHARE UPDATE EXCLUSIVE lock.
SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
SET COMPRESSION compression_method
ADD table_constraint [ NOT VALID ]
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
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.
ALTER CONSTRAINT
VALIDATE CONSTRAINT
This command acquires a SHARE UPDATE EXCLUSIVE lock.
DROP CONSTRAINT [ IF EXISTS ]
DISABLE/ENABLE [ REPLICA | ALWAYS ] TRIGGER
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
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
NO FORCE/FORCE ROW LEVEL SECURITY
CLUSTER ON
Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock.
SET WITHOUT CLUSTER
Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock.
SET WITHOUT OIDS
SET ACCESS METHOD
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
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 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] [, ... ] )
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 [, ... ] )
INHERIT parent_table
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
OF type_name
NOT OF
OWNER TO
REPLICA IDENTITY
DEFAULT
USING INDEX index_name
FULL
NOTHING
RENAME
SET SCHEMA
ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }
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 (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 5.12.2.2.
DETACH PARTITION partition_name [ CONCURRENTLY | FINALIZE ]
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.
PARAMETERS
IF EXISTS
name
column_name
new_column_name
new_name
data_type
table_constraint
constraint_name
CASCADE
RESTRICT
trigger_name
ALL
USER
index_name
storage_parameter
value
parent_table
new_owner
new_access_method
new_tablespace
new_schema
partition_name
partition_bound_spec
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
\n
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
\n
ADD COLUMN status varchar(30) DEFAULT 'old',
\n
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
\n
ALTER COLUMN address TYPE varchar(80),
\n
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
\n
ALTER COLUMN foo_timestamp SET DATA TYPE timestamp with time zone
\n
USING
\n
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
\n
ALTER COLUMN foo_timestamp DROP DEFAULT,
\n
ALTER COLUMN foo_timestamp TYPE timestamp with time zone
\n
USING
\n
timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',
\n
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,
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ADD CONSTRAINT distributors_pkey PRIMARY KEY USING INDEX dist_id_temp_idx;To attach a partition to a range-partitioned table:
ALTER TABLE measurement
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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
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ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');To attach a partition to a hash-partitioned table:
ALTER TABLE orders
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ATTACH PARTITION orders_p4 FOR VALUES WITH (MODULUS 4, REMAINDER 3);To attach a default partition to a partitioned table:
ALTER TABLE cities
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ATTACH PARTITION cities_partdef DEFAULT;To detach a partition from a partitioned table:
ALTER TABLE measurement
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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))