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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
           CLUSTER ON index_name
           SET WITHOUT CLUSTER
           SET WITH OIDS
           SET WITHOUT OIDS
           SET ( storage_parameter = value [, ... ] )
           RESET ( storage_parameter [, ... ] )
           INHERIT parent_table
           NO INHERIT parent_table
           OF type_name
           NOT OF
           OWNER TO new_owner
           SET TABLESPACE new_tablespace
           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.

       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 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 59.2, “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.

       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 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 ( 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.

       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)).

       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

       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.

       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 (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))



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