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 ] whereaction
is one of: ADD [ COLUMN ]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 | DROP } NOT NULL ALTER [ COLUMN ]column_name
SET STATISTICSinteger
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 } 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
CLUSTER ONindex_name
SET WITHOUT CLUSTER SET WITH OIDS SET WITHOUT OIDS SET (storage_parameter
=value
[, ... ] ) RESET (storage_parameter
[, ... ] ) INHERITparent_table
NO INHERITparent_table
OFtype_name
NOT OF OWNER TOnew_owner
SET TABLESPACEnew_tablespace
REPLICA IDENTITY {DEFAULT | USING INDEXindex_name
| FULL | NOTHING} andtable_constraint_using_index
is: [ CONSTRAINTconstraint_name
] { UNIQUE | PRIMARY KEY } USING INDEXindex_name
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
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 held
unless explicitly noted. When multiple subcommands are listed, the lock
held will be the strictest one required from any subcommand.
ADD COLUMN
This form adds a new column to the table, using the same syntax as CREATE TABLE(7).
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. 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.
IF EXISTS
Do not throw an error if the table does not exist. A notice is issued in this case.
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.
SET
/DROP DEFAULT
These forms set or remove the default value for a column. Default values only apply in subsequent INSERT or UPDATE commands; they do 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. You can only use SET
NOT NULL
when the column contains no null values.
SET STATISTICS
This form sets the per-column statistics-gathering target for subsequent ANALYZE(7) 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 the section called “Statistics Used by the Planner”.
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(7)
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 the section called “Statistics Used by the Planner”.
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 the section called “TOAST” for more information.
ADD table_constraint
[ NOT VALID ]
This form adds a new constraint to a table using the same syntax as
CREATE TABLE(7), plus the option NOT
VALID
, which is currently only allowed for foreign key
and CHECK constraints.
If the constraint is marked NOT VALID
, the
potentially-lengthy initial check to verify that all rows in the table
satisfy the constraint 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; and they'll fail unless the new row matches the
specified check constraints). 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.
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.
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.
Validation can be a long process on larger tables. The value of separating validation from initial creation is that you can defer validation to less busy times, or can be used to give additional time to correct pre-existing errors while preventing new errors. Note also that validation on its own does not prevent normal write commands against the table while it runs.
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.
DROP CONSTRAINT [ IF EXISTS ]
This form drops the specified constraint on a table.
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 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 mode.
DISABLE
/ENABLE [ REPLICA | ALWAYS ] RULE
These forms configure the firing of rewrite rules belonging to the table.
A disabled rule is still known to the system, but is not applied
during query rewriting. The semantics are as for disabled/enabled
triggers. This 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.
CLUSTER ON
This form selects the default index for future CLUSTER(7) 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(7) 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 WITH OIDS
This form adds an oid
system column to the
table (see the section called “System Columns”).
It does nothing if the table already has OIDs.
Note that this is not equivalent to ADD COLUMN oid oid
;
that would add a normal column that happened to be named
oid
, not a system column.
SET WITHOUT OIDS
This form removes the oid
system column from the
table. This is exactly equivalent to
DROP COLUMN oid RESTRICT
,
except that it will not complain if there is already no
oid
column.
SET ( storage_parameter
= value
[, ... ] )
This form changes one or more storage parameters for the table. See Storage Parameters 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(7) or one of the forms of ALTER TABLE that forces a table rewrite.
While CREATE TABLE allows OIDS
to be specified
in the WITH (
syntax,
ALTER TABLE does not treat storage_parameter
)OIDS
as a
storage parameter. Instead use the SET WITH OIDS
and SET WITHOUT OIDS
forms to change OID status.
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 presence of
an oid
system column is permitted to differ. 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
This form changes the owner of the table, sequence, view, materialized view, or foreign table to the specified user.
SET TABLESPACE
This form changes the table's tablespace to the specified tablespace and
moves the data file(s) associated with the table to the new tablespace.
Indexes on the table, if any, are not moved; but they can be moved
separately with additional SET TABLESPACE
commands.
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(7).
REPLICA IDENTITY
This form changes the information which is written to the write-ahead log
to identify rows which are updated or deleted. This option has no effect
except when logical replication is in use. DEFAULT
(the default for non-system tables) records the
old values of the columns of the primary key, if any. USING INDEX
records the old values of the columns covered by the named index, which
must be unique, not partial, not deferrable, and include only columns marked
NOT NULL
. 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.)
In all cases, no old values are logged unless at least one of the columns
that would be logged differs between the old and new versions of the row.
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.
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.
All the actions except RENAME
,
SET TABLESPACE
and SET SCHEMA
can be combined into
a list of multiple alterations to apply in parallel. For example, it
is possible to add several columns and/or alter the type of several
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.
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.
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).
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_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.
The key word COLUMN
is noise and can be omitted.
When a column is added with ADD COLUMN
, all existing
rows in the table are initialized with the column's default value
(NULL if no DEFAULT
clause is specified).
If there is no DEFAULT
clause, this is merely a metadata
change and does not require any immediate update of the table's data;
the added NULL values are supplied on readout, instead.
Adding a column with a DEFAULT
clause 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;
but any indexes on the affected columns must still be rebuilt. Adding or
removing a system oid
column also requires rewriting the entire
table. 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.
The main reason for providing the option to specify multiple changes in a single ALTER TABLE is that multiple table scans or rewrites can thereby be combined into a single pass over the table.
The DROP COLUMN
form does not physically remove
the column, but simply makes it invisible to SQL operations. Subsequent
insert and update operations in the table will store a null value for the
column. Thus, dropping a column is quick but it will not immediately
reduce the on-disk size of your table, as the space occupied
by the dropped column is not reclaimed. The space will be
reclaimed over time as existing rows are updated. (These statements do
not apply when dropping the system oid
column; that is done
with an immediate rewrite.)
To force an immediate rewrite of the table, you can use VACUUM FULL, CLUSTER(7) or one of the forms of ALTER TABLE that forces a rewrite. This results in no semantically-visible change in the table, but gets rid of no-longer-useful data.
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, or rename an inherited constraint in the parent table without doing the same to the descendants. That is, ALTER TABLE ONLY will be rejected. This ensures that the descendants always have columns matching the parent.
A recursive DROP COLUMN
operation will remove a
descendant table's column only if the descendant does not inherit
that column from any other parents and never had an independent
definition of the column. A nonrecursive DROP
COLUMN
(i.e., ALTER TABLE ONLY ... DROP
COLUMN) never removes any descendant columns, but
instead marks them as independently defined rather than inherited.
The TRIGGER
, CLUSTER
, OWNER
,
and TABLESPACE
actions never recurse to descendant tables;
that is, they always act as though ONLY
were specified.
Adding a 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(7) for a further description of valid parameters. Chapter 5, Data Definition has further information on inheritance.
To add a column of type varchar to a table:
ALTER TABLE distributors ADD COLUMN address varchar(30);
To drop a column from a table:
ALTER TABLE distributors DROP COLUMN address RESTRICT;
To change the types of two existing columns in one operation:
ALTER TABLE distributors ALTER COLUMN address TYPE varchar(80), ALTER COLUMN name TYPE varchar(100);
To change an integer column containing UNIX timestamps to timestamp
with time zone via a USING
clause:
ALTER TABLE foo ALTER COLUMN foo_timestamp 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;
The forms ADD
(without USING INDEX
),
DROP
, SET DEFAULT
,
and SET DATA TYPE
(without USING
)
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.