Provided by: postgresql-client-9.5_9.5.2-1_amd64 bug

NAME

       ALTER_TABLE - change the definition of a table

SYNOPSIS

       ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
           action [, ... ]
       ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
           RENAME [ COLUMN ] column_name TO new_column_name
       ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
           RENAME CONSTRAINT constraint_name TO new_constraint_name
       ALTER TABLE [ IF EXISTS ] name
           RENAME TO new_name
       ALTER TABLE [ IF EXISTS ] name
           SET SCHEMA new_schema
       ALTER TABLE ALL IN TABLESPACE name [ OWNED BY role_name [, ... ] ]
           SET TABLESPACE new_tablespace [ NOWAIT ]

       where action is one of:

           ADD [ COLUMN ] column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
           DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ]
           ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type [ COLLATE collation ] [ USING expression ]
           ALTER [ COLUMN ] column_name SET DEFAULT expression
           ALTER [ COLUMN ] column_name DROP DEFAULT
           ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL
           ALTER [ COLUMN ] column_name SET STATISTICS integer
           ALTER [ COLUMN ] column_name SET ( attribute_option = value [, ... ] )
           ALTER [ COLUMN ] column_name RESET ( attribute_option [, ... ] )
           ALTER [ COLUMN ] column_name SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
           ADD table_constraint [ NOT VALID ]
           ADD table_constraint_using_index
           ALTER CONSTRAINT constraint_name [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
           VALIDATE CONSTRAINT constraint_name
           DROP CONSTRAINT [ IF EXISTS ]  constraint_name [ RESTRICT | CASCADE ]
           DISABLE TRIGGER [ trigger_name | ALL | USER ]
           ENABLE TRIGGER [ trigger_name | ALL | USER ]
           ENABLE REPLICA TRIGGER trigger_name
           ENABLE ALWAYS TRIGGER trigger_name
           DISABLE RULE rewrite_rule_name
           ENABLE RULE rewrite_rule_name
           ENABLE REPLICA RULE rewrite_rule_name
           ENABLE ALWAYS RULE rewrite_rule_name
           DISABLE ROW LEVEL SECURITY
           ENABLE ROW LEVEL SECURITY
           FORCE ROW LEVEL SECURITY
           NO FORCE ROW LEVEL SECURITY
           CLUSTER ON index_name
           SET WITHOUT CLUSTER
           SET WITH OIDS
           SET WITHOUT OIDS
           SET TABLESPACE new_tablespace
           SET { LOGGED | UNLOGGED }
           SET ( storage_parameter = value [, ... ] )
           RESET ( storage_parameter [, ... ] )
           INHERIT parent_table
           NO INHERIT parent_table
           OF type_name
           NOT OF
           OWNER TO { new_owner | CURRENT_USER | SESSION_USER }
           REPLICA IDENTITY { DEFAULT | USING INDEX index_name | FULL | NOTHING }

       and table_constraint_using_index is:

           [ CONSTRAINT constraint_name ]
           { UNIQUE | PRIMARY KEY } USING INDEX index_name
           [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

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 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
           (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.

       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 Section 14.2, “Statistics Used by the Planner”, in the documentation.

           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 Section
           14.2, “Statistics Used by the Planner”, in the documentation.

           Changing per-attribute options acquires a SHARE UPDATE EXCLUSIVE lock.

       SET STORAGE
           This form sets the storage mode for a column. This controls whether this column is
           held inline or in a secondary TOAST table, and whether the data should be compressed
           or not.  PLAIN must be used for fixed-length values such as integer and is inline,
           uncompressed.  MAIN is for inline, compressible data.  EXTERNAL is for external,
           uncompressed data, and EXTENDED is for external, compressed data.  EXTENDED is the
           default for most data types that support non-PLAIN storage. Use of EXTERNAL will make
           substring operations on very large text and bytea values run faster, at the penalty of
           increased storage space. Note that SET STORAGE doesn't itself change anything in the
           table, it just sets the strategy to be pursued during future table updates. See
           Section 63.2, “TOAST”, in the documentation for more information.

       ADD table_constraint [ NOT VALID ]
           This form adds a new constraint to a table using the same syntax as CREATE TABLE
           (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.

               Note
               Adding a constraint using an existing index can be helpful in situations where a
               new constraint needs to be added without blocking table updates for a long time.
               To do that, create the index using CREATE INDEX CONCURRENTLY, and then install it
               as an official constraint using this syntax. See the example below.

       ALTER CONSTRAINT
           This form alters the attributes of a constraint that was previously created. Currently
           only foreign key constraints may be altered.

       VALIDATE CONSTRAINT
           This form validates a foreign key or check constraint that was previously created as
           NOT VALID, by scanning the table to ensure there are no rows for which the constraint
           is not satisfied. Nothing happens if the constraint is already marked valid.

           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.

           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.

       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 (CREATE_POLICY(7)).

       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
           (CREATE_POLICY(7)).

       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 Section 5.4, “System Columns”,
           in the documentation). 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 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 (CREATE_TABLESPACE(7)).

       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.

       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.

               Note
               While CREATE TABLE allows OIDS to be specified in the WITH (storage_parameter)
               syntax, ALTER TABLE does not treat 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.

       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.

PARAMETERS

       IF EXISTS
           Do not throw an error if the table does not exist. A notice is issued in this case.

       name
           The name (optionally schema-qualified) of an existing table to alter. If ONLY is
           specified before the table name, only that table is altered. If ONLY is not specified,
           the table and all its descendant tables (if any) are altered. Optionally, * can be
           specified after the table name to explicitly indicate that descendant tables are
           included.

       column_name
           Name of a new or existing column.

       new_column_name
           New name for an existing column.

       new_name
           New name for the table.

       data_type
           Data type of the new column, or new data type for an existing column.

       table_constraint
           New table constraint for the table.

       constraint_name
           Name of a new or existing constraint.

       CASCADE
           Automatically drop objects that depend on the dropped column or constraint (for
           example, views referencing the column).

       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.

NOTES

       The key word COLUMN is noise and can be omitted.

       When a column is added with ADD COLUMN, all existing rows in the table are 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, but does not require a table rewrite.

       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 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 13.5, “Caveats”, in the documentation 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, 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 (CREATE_TABLE(7)) for a further description of valid parameters.
       Chapter 5, Data Definition, in the documentation has further information on inheritance.

EXAMPLES

       To add a column of type varchar to a table:

           ALTER TABLE distributors ADD COLUMN address varchar(30);

       To drop a column from a table:

           ALTER TABLE distributors DROP COLUMN address RESTRICT;

       To change the types of two existing columns in one operation:

           ALTER TABLE distributors
               ALTER COLUMN address TYPE varchar(80),
               ALTER COLUMN name TYPE varchar(100);

       To change an integer column containing Unix timestamps to timestamp with time zone via a
       USING clause:

           ALTER TABLE foo
               ALTER COLUMN foo_timestamp 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;

COMPATIBILITY

       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.

SEE ALSO

       CREATE TABLE (CREATE_TABLE(7))