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><H1
><A
NAME="SQL-ALTERTABLE"
></A
>ALTER TABLE</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN75980"
></A
><H2
>Name</H2
>ALTER TABLE -- change the definition of a table</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN75983"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>ALTER TABLE [ IF EXISTS ] [ ONLY ] <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> [ * ]
<TT
CLASS="REPLACEABLE"
><I
>action</I
></TT
> [, ... ]
ALTER TABLE [ IF EXISTS ] [ ONLY ] <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> [ * ]
RENAME [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> TO <TT
CLASS="REPLACEABLE"
><I
>new_column_name</I
></TT
>
ALTER TABLE [ IF EXISTS ] [ ONLY ] <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> [ * ]
RENAME CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> TO <TT
CLASS="REPLACEABLE"
><I
>new_constraint_name</I
></TT
>
ALTER TABLE [ IF EXISTS ] <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
>
RENAME TO <TT
CLASS="REPLACEABLE"
><I
>new_name</I
></TT
>
ALTER TABLE [ IF EXISTS ] <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
>
SET SCHEMA <TT
CLASS="REPLACEABLE"
><I
>new_schema</I
></TT
>
ALTER TABLE ALL IN TABLESPACE <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> [ OWNED BY <TT
CLASS="REPLACEABLE"
><I
>role_name</I
></TT
> [, ... ] ]
SET TABLESPACE <TT
CLASS="REPLACEABLE"
><I
>new_tablespace</I
></TT
> [ NOWAIT ]
<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>where <TT
CLASS="REPLACEABLE"
><I
>action</I
></TT
> is one of:</SPAN
></SPAN
>
ADD [ COLUMN ] [ IF NOT EXISTS ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>data_type</I
></TT
> [ COLLATE <TT
CLASS="REPLACEABLE"
><I
>collation</I
></TT
> ] [ <TT
CLASS="REPLACEABLE"
><I
>column_constraint</I
></TT
> [ ... ] ]
DROP [ COLUMN ] [ IF EXISTS ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> [ RESTRICT | CASCADE ]
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> [ SET DATA ] TYPE <TT
CLASS="REPLACEABLE"
><I
>data_type</I
></TT
> [ COLLATE <TT
CLASS="REPLACEABLE"
><I
>collation</I
></TT
> ] [ USING <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ]
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> SET DEFAULT <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> DROP DEFAULT
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> { SET | DROP } NOT NULL
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> SET STATISTICS <TT
CLASS="REPLACEABLE"
><I
>integer</I
></TT
>
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> SET ( <TT
CLASS="REPLACEABLE"
><I
>attribute_option</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
> [, ... ] )
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> RESET ( <TT
CLASS="REPLACEABLE"
><I
>attribute_option</I
></TT
> [, ... ] )
ALTER [ COLUMN ] <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
ADD <TT
CLASS="REPLACEABLE"
><I
>table_constraint</I
></TT
> [ NOT VALID ]
ADD <TT
CLASS="REPLACEABLE"
><I
>table_constraint_using_index</I
></TT
>
ALTER CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
VALIDATE CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
>
DROP CONSTRAINT [ IF EXISTS ] <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> [ RESTRICT | CASCADE ]
DISABLE TRIGGER [ <TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
> | ALL | USER ]
ENABLE TRIGGER [ <TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
> | ALL | USER ]
ENABLE REPLICA TRIGGER <TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
>
ENABLE ALWAYS TRIGGER <TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
>
DISABLE RULE <TT
CLASS="REPLACEABLE"
><I
>rewrite_rule_name</I
></TT
>
ENABLE RULE <TT
CLASS="REPLACEABLE"
><I
>rewrite_rule_name</I
></TT
>
ENABLE REPLICA RULE <TT
CLASS="REPLACEABLE"
><I
>rewrite_rule_name</I
></TT
>
ENABLE ALWAYS RULE <TT
CLASS="REPLACEABLE"
><I
>rewrite_rule_name</I
></TT
>
DISABLE ROW LEVEL SECURITY
ENABLE ROW LEVEL SECURITY
FORCE ROW LEVEL SECURITY
NO FORCE ROW LEVEL SECURITY
CLUSTER ON <TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
>
SET WITHOUT CLUSTER
SET WITH OIDS
SET WITHOUT OIDS
SET TABLESPACE <TT
CLASS="REPLACEABLE"
><I
>new_tablespace</I
></TT
>
SET { LOGGED | UNLOGGED }
SET ( <TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
> [= <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>] [, ... ] )
RESET ( <TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
> [, ... ] )
INHERIT <TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
>
NO INHERIT <TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
>
OF <TT
CLASS="REPLACEABLE"
><I
>type_name</I
></TT
>
NOT OF
OWNER TO { <TT
CLASS="REPLACEABLE"
><I
>new_owner</I
></TT
> | CURRENT_USER | SESSION_USER }
REPLICA IDENTITY { DEFAULT | USING INDEX <TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
> | FULL | NOTHING }
<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>and <TT
CLASS="REPLACEABLE"
><I
>table_constraint_using_index</I
></TT
> is:</SPAN
></SPAN
>
[ CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> ]
{ UNIQUE | PRIMARY KEY } USING INDEX <TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
>
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN76050"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> 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 <TT
CLASS="LITERAL"
>ACCESS EXCLUSIVE</TT
> lock is
acquired unless explicitly noted. When multiple subcommands are given, the
lock acquired will be the strictest one required by any subcommand.
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>ADD COLUMN [ IF NOT EXISTS ]</TT
></DT
><DD
><P
> This form adds a new column to the table, using the same syntax as
<A
HREF="sql-createtable.html"
>CREATE TABLE</A
>. If <TT
CLASS="LITERAL"
>IF NOT EXISTS</TT
>
is specified and a column already exists with this name,
no error is thrown.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DROP COLUMN [ IF EXISTS ]</TT
></DT
><DD
><P
> 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 <TT
CLASS="LITERAL"
>CASCADE</TT
> if
anything outside the table depends on the column, for example,
foreign key references or views.
If <TT
CLASS="LITERAL"
>IF EXISTS</TT
> is specified and the column
does not exist, no error is thrown. In this case a notice
is issued instead.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET DATA TYPE</TT
></DT
><DD
><P
> 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 <TT
CLASS="LITERAL"
>COLLATE</TT
> clause specifies a collation
for the new column; if omitted, the collation is the default for the
new column type.
The optional <TT
CLASS="LITERAL"
>USING</TT
>
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 <TT
CLASS="LITERAL"
>USING</TT
>
clause must be provided if there is no implicit or assignment
cast from old to new type.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET</TT
>/<TT
CLASS="LITERAL"
>DROP DEFAULT</TT
></DT
><DD
><P
> These forms set or remove the default value for a column.
Default values only apply in subsequent <TT
CLASS="COMMAND"
>INSERT</TT
>
or <TT
CLASS="COMMAND"
>UPDATE</TT
> commands; they do not cause rows already in the
table to change.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET</TT
>/<TT
CLASS="LITERAL"
>DROP NOT NULL</TT
></DT
><DD
><P
> These forms change whether a column is marked to allow null
values or to reject null values. You can only use <TT
CLASS="LITERAL"
>SET
NOT NULL</TT
> when the column contains no null values.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET STATISTICS</TT
></DT
><DD
><P
> This form
sets the per-column statistics-gathering target for subsequent
<A
HREF="sql-analyze.html"
>ANALYZE</A
> 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 (<A
HREF="runtime-config-query.html#GUC-DEFAULT-STATISTICS-TARGET"
>default_statistics_target</A
>).
For more information on the use of statistics by the
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> query planner, refer to
<A
HREF="planner-stats.html"
>Section 14.2</A
>.
</P
><P
> <TT
CLASS="LITERAL"
>SET STATISTICS</TT
> acquires a
<TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET ( <TT
CLASS="REPLACEABLE"
><I
>attribute_option</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
> [, ... ] )</TT
><BR><TT
CLASS="LITERAL"
>RESET ( <TT
CLASS="REPLACEABLE"
><I
>attribute_option</I
></TT
> [, ... ] )</TT
></DT
><DD
><P
> This form sets or resets per-attribute options. Currently, the only
defined per-attribute options are <TT
CLASS="LITERAL"
>n_distinct</TT
> and
<TT
CLASS="LITERAL"
>n_distinct_inherited</TT
>, which override the
number-of-distinct-values estimates made by subsequent
<A
HREF="sql-analyze.html"
>ANALYZE</A
>
operations. <TT
CLASS="LITERAL"
>n_distinct</TT
> affects the statistics for the table
itself, while <TT
CLASS="LITERAL"
>n_distinct_inherited</TT
> affects the statistics
gathered for the table plus its inheritance children. When set to a
positive value, <TT
CLASS="COMMAND"
>ANALYZE</TT
> 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, <TT
CLASS="COMMAND"
>ANALYZE</TT
> 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 <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> query
planner, refer to <A
HREF="planner-stats.html"
>Section 14.2</A
>.
</P
><P
> Changing per-attribute options acquires a
<TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET STORAGE</TT
>
</DT
><DD
><P
> This form sets the storage mode for a column. This controls whether this
column is held inline or in a secondary <ACRONYM
CLASS="ACRONYM"
>TOAST</ACRONYM
> table, and
whether the data
should be compressed or not. <TT
CLASS="LITERAL"
>PLAIN</TT
> must be used
for fixed-length values such as <TT
CLASS="TYPE"
>integer</TT
> and is
inline, uncompressed. <TT
CLASS="LITERAL"
>MAIN</TT
> is for inline,
compressible data. <TT
CLASS="LITERAL"
>EXTERNAL</TT
> is for external,
uncompressed data, and <TT
CLASS="LITERAL"
>EXTENDED</TT
> is for external,
compressed data. <TT
CLASS="LITERAL"
>EXTENDED</TT
> is the default for most
data types that support non-<TT
CLASS="LITERAL"
>PLAIN</TT
> storage.
Use of <TT
CLASS="LITERAL"
>EXTERNAL</TT
> will make substring operations on
very large <TT
CLASS="TYPE"
>text</TT
> and <TT
CLASS="TYPE"
>bytea</TT
> values run faster,
at the penalty of increased storage space. Note that
<TT
CLASS="LITERAL"
>SET STORAGE</TT
> doesn't itself change anything in the table,
it just sets the strategy to be pursued during future table updates.
See <A
HREF="storage-toast.html"
>Section 65.2</A
> for more information.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>ADD <TT
CLASS="REPLACEABLE"
><I
>table_constraint</I
></TT
> [ NOT VALID ]</TT
></DT
><DD
><P
> This form adds a new constraint to a table using the same constraint
syntax as <A
HREF="sql-createtable.html"
>CREATE TABLE</A
>, plus the option <TT
CLASS="LITERAL"
>NOT
VALID</TT
>, which is currently only allowed for foreign key
and CHECK constraints.
</P
><P
> Normally, this form will cause a scan of the table to verify that all
existing rows in the table satisfy the new constraint. But if
the <TT
CLASS="LITERAL"
>NOT VALID</TT
> option is used, this
potentially-lengthy scan is skipped. The constraint will still be
enforced against subsequent inserts or updates (that is, they'll fail
unless there is a matching row in the referenced table, in the case
of foreign keys, or they'll fail unless the new row matches the
specified check condition). But the
database will not assume that the constraint holds for all rows in
the table, until it is validated by using the <TT
CLASS="LITERAL"
>VALIDATE
CONSTRAINT</TT
> option.
See <A
HREF="sql-altertable.html#SQL-ALTERTABLE-NOTES"
><I
>Notes</I
></A
> below for more information
about using the <TT
CLASS="LITERAL"
>NOT VALID</TT
> option.
</P
><P
> Although most forms of <TT
CLASS="LITERAL"
>ADD
<TT
CLASS="REPLACEABLE"
><I
>table_constraint</I
></TT
></TT
>
require an <TT
CLASS="LITERAL"
>ACCESS EXCLUSIVE</TT
> lock, <TT
CLASS="LITERAL"
>ADD
FOREIGN KEY</TT
> requires only a <TT
CLASS="LITERAL"
>SHARE ROW
EXCLUSIVE</TT
> lock. Note that <TT
CLASS="LITERAL"
>ADD FOREIGN KEY</TT
>
also acquires a <TT
CLASS="LITERAL"
>SHARE ROW EXCLUSIVE</TT
> lock on the
referenced table, in addition to the lock on the table on which the
constraint is declared.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>ADD <TT
CLASS="REPLACEABLE"
><I
>table_constraint_using_index</I
></TT
></TT
></DT
><DD
><P
> This form adds a new <TT
CLASS="LITERAL"
>PRIMARY KEY</TT
> or <TT
CLASS="LITERAL"
>UNIQUE</TT
>
constraint to a table based on an existing unique index. All the
columns of the index will be included in the constraint.
</P
><P
> 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 <TT
CLASS="LITERAL"
>ADD PRIMARY KEY</TT
> or <TT
CLASS="LITERAL"
>ADD UNIQUE</TT
>
command.
</P
><P
> If <TT
CLASS="LITERAL"
>PRIMARY KEY</TT
> is specified, and the index's columns are not
already marked <TT
CLASS="LITERAL"
>NOT NULL</TT
>, then this command will attempt to
do <TT
CLASS="LITERAL"
>ALTER COLUMN SET NOT NULL</TT
> 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.
</P
><P
> 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.
</P
><P
> After this command is executed, the index is <SPAN
CLASS="QUOTE"
>"owned"</SPAN
> by the
constraint, in the same way as if the index had been built by
a regular <TT
CLASS="LITERAL"
>ADD PRIMARY KEY</TT
> or <TT
CLASS="LITERAL"
>ADD UNIQUE</TT
>
command. In particular, dropping the constraint will make the index
disappear too.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> 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
<TT
CLASS="COMMAND"
>CREATE INDEX CONCURRENTLY</TT
>, and then install it as an
official constraint using this syntax. See the example below.
</P
></BLOCKQUOTE
></DIV
></DD
><DT
><TT
CLASS="LITERAL"
>ALTER CONSTRAINT</TT
></DT
><DD
><P
> This form alters the attributes of a constraint that was previously
created. Currently only foreign key constraints may be altered.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>VALIDATE CONSTRAINT</TT
></DT
><DD
><P
> This form validates a foreign key or check constraint that was
previously created as <TT
CLASS="LITERAL"
>NOT VALID</TT
>, by scanning the
table to ensure there are no rows for which the constraint is not
satisfied. Nothing happens if the constraint is already marked valid.
(See <A
HREF="sql-altertable.html#SQL-ALTERTABLE-NOTES"
><I
>Notes</I
></A
> below for an explanation of the
usefulness of this command.)
</P
><P
> This command acquires a <TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DROP CONSTRAINT [ IF EXISTS ]</TT
></DT
><DD
><P
> This form drops the specified constraint on a table.
If <TT
CLASS="LITERAL"
>IF EXISTS</TT
> is specified and the constraint
does not exist, no error is thrown. In this case a notice is issued instead.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DISABLE</TT
>/<TT
CLASS="LITERAL"
>ENABLE [ REPLICA | ALWAYS ] TRIGGER</TT
></DT
><DD
><P
> 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 <A
HREF="runtime-config-client.html#GUC-SESSION-REPLICATION-ROLE"
>session_replication_role</A
>. Simply enabled
triggers will fire when the replication role is <SPAN
CLASS="QUOTE"
>"origin"</SPAN
>
(the default) or <SPAN
CLASS="QUOTE"
>"local"</SPAN
>. Triggers configured as <TT
CLASS="LITERAL"
>ENABLE
REPLICA</TT
> will only fire if the session is in <SPAN
CLASS="QUOTE"
>"replica"</SPAN
>
mode, and triggers configured as <TT
CLASS="LITERAL"
>ENABLE ALWAYS</TT
> will
fire regardless of the current replication mode.
</P
><P
> This command acquires a <TT
CLASS="LITERAL"
>SHARE ROW EXCLUSIVE</TT
> lock.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DISABLE</TT
>/<TT
CLASS="LITERAL"
>ENABLE [ REPLICA | ALWAYS ] RULE</TT
></DT
><DD
><P
> 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 <TT
CLASS="LITERAL"
>ON SELECT</TT
> rules, which
are always applied in order to keep views working even if the current
session is in a non-default replication role.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DISABLE</TT
>/<TT
CLASS="LITERAL"
>ENABLE ROW LEVEL SECURITY</TT
></DT
><DD
><P
> 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
<A
HREF="sql-createpolicy.html"
>CREATE POLICY</A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NO FORCE</TT
>/<TT
CLASS="LITERAL"
>FORCE ROW LEVEL SECURITY</TT
></DT
><DD
><P
> 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
<A
HREF="sql-createpolicy.html"
>CREATE POLICY</A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CLUSTER ON</TT
></DT
><DD
><P
> This form selects the default index for future
<A
HREF="sql-cluster.html"
>CLUSTER</A
>
operations. It does not actually re-cluster the table.
</P
><P
> Changing cluster options acquires a <TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET WITHOUT CLUSTER</TT
></DT
><DD
><P
> This form removes the most recently used
<A
HREF="sql-cluster.html"
>CLUSTER</A
>
index specification from the table. This affects
future cluster operations that don't specify an index.
</P
><P
> Changing cluster options acquires a <TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET WITH OIDS</TT
></DT
><DD
><P
> This form adds an <TT
CLASS="LITERAL"
>oid</TT
> system column to the
table (see <A
HREF="ddl-system-columns.html"
>Section 5.4</A
>).
It does nothing if the table already has OIDs.
</P
><P
> Note that this is not equivalent to <TT
CLASS="LITERAL"
>ADD COLUMN oid oid</TT
>;
that would add a normal column that happened to be named
<TT
CLASS="LITERAL"
>oid</TT
>, not a system column.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET WITHOUT OIDS</TT
></DT
><DD
><P
> This form removes the <TT
CLASS="LITERAL"
>oid</TT
> system column from the
table. This is exactly equivalent to
<TT
CLASS="LITERAL"
>DROP COLUMN oid RESTRICT</TT
>,
except that it will not complain if there is already no
<TT
CLASS="LITERAL"
>oid</TT
> column.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET TABLESPACE</TT
></DT
><DD
><P
> 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 <TT
CLASS="LITERAL"
>SET TABLESPACE</TT
> commands.
All tables in the current database in a tablespace can be moved by using
the <TT
CLASS="LITERAL"
>ALL IN TABLESPACE</TT
> form, which will lock all tables
to be moved first and then move each one. This form also supports
<TT
CLASS="LITERAL"
>OWNED BY</TT
>, which will only move tables owned by the
roles specified. If the <TT
CLASS="LITERAL"
>NOWAIT</TT
> 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 <TT
CLASS="COMMAND"
>ALTER DATABASE</TT
> or explicit
<TT
CLASS="COMMAND"
>ALTER TABLE</TT
> invocations instead if desired. The
<TT
CLASS="LITERAL"
>information_schema</TT
> relations are not considered part
of the system catalogs and will be moved.
See also
<A
HREF="sql-createtablespace.html"
>CREATE TABLESPACE</A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET { LOGGED | UNLOGGED }</TT
></DT
><DD
><P
> This form changes the table from unlogged to logged or vice-versa
(see <A
HREF="sql-createtable.html#SQL-CREATETABLE-UNLOGGED"
><I
CLASS="TERM"
><TT
CLASS="LITERAL"
>UNLOGGED</TT
></I
></A
>). It cannot be applied
to a temporary table.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET ( <TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
> [= <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>] [, ... ] )</TT
></DT
><DD
><P
> This form changes one or more storage parameters for the table. See
<A
HREF="sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS"
><I
>Storage Parameters</I
></A
>
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 <A
HREF="sql-vacuum.html"
>VACUUM
FULL</A
>, <A
HREF="sql-cluster.html"
>CLUSTER</A
> or one of the forms
of <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> that forces a table rewrite.
</P
><P
> Changing fillfactor and autovacuum storage parameters acquires a <TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> While <TT
CLASS="COMMAND"
>CREATE TABLE</TT
> allows <TT
CLASS="LITERAL"
>OIDS</TT
> to be specified
in the <TT
CLASS="LITERAL"
>WITH (<TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
>)</TT
> syntax,
<TT
CLASS="COMMAND"
>ALTER TABLE</TT
> does not treat <TT
CLASS="LITERAL"
>OIDS</TT
> as a
storage parameter. Instead use the <TT
CLASS="LITERAL"
>SET WITH OIDS</TT
>
and <TT
CLASS="LITERAL"
>SET WITHOUT OIDS</TT
> forms to change OID status.
</P
></BLOCKQUOTE
></DIV
></DD
><DT
><TT
CLASS="LITERAL"
>RESET ( <TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
> [, ... ] )</TT
></DT
><DD
><P
> This form resets one or more storage parameters to their
defaults. As with <TT
CLASS="LITERAL"
>SET</TT
>, a table rewrite might be
needed to update the table entirely.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>INHERIT <TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
></TT
></DT
><DD
><P
> 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 <TT
CLASS="LITERAL"
>NOT NULL</TT
> constraints in the parent
then they must also have <TT
CLASS="LITERAL"
>NOT NULL</TT
> constraints in the
child.
</P
><P
> There must also be matching child-table constraints for all
<TT
CLASS="LITERAL"
>CHECK</TT
> constraints of the parent, except those
marked non-inheritable (that is, created with <TT
CLASS="LITERAL"
>ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT</TT
>)
in the parent, which are ignored; all child-table constraints matched
must not be marked non-inheritable.
Currently
<TT
CLASS="LITERAL"
>UNIQUE</TT
>, <TT
CLASS="LITERAL"
>PRIMARY KEY</TT
>, and
<TT
CLASS="LITERAL"
>FOREIGN KEY</TT
> constraints are not considered, but
this might change in the future.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NO INHERIT <TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
></TT
></DT
><DD
><P
> 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.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>OF <TT
CLASS="REPLACEABLE"
><I
>type_name</I
></TT
></TT
></DT
><DD
><P
> This form links the table to a composite type as though <TT
CLASS="COMMAND"
>CREATE
TABLE OF</TT
> had formed it. The table's list of column names and types
must precisely match that of the composite type; the presence of
an <TT
CLASS="LITERAL"
>oid</TT
> system column is permitted to differ. The table must
not inherit from any other table. These restrictions ensure
that <TT
CLASS="COMMAND"
>CREATE TABLE OF</TT
> would permit an equivalent table
definition.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NOT OF</TT
></DT
><DD
><P
> This form dissociates a typed table from its type.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>OWNER</TT
></DT
><DD
><P
> This form changes the owner of the table, sequence, view, materialized view,
or foreign table to the specified user.
</P
></DD
><DT
><A
NAME="SQL-CREATETABLE-REPLICA-IDENTITY"
></A
><TT
CLASS="LITERAL"
>REPLICA IDENTITY</TT
></DT
><DD
><P
> 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. <TT
CLASS="LITERAL"
>DEFAULT</TT
>
(the default for non-system tables) records the
old values of the columns of the primary key, if any. <TT
CLASS="LITERAL"
>USING INDEX</TT
>
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
<TT
CLASS="LITERAL"
>NOT NULL</TT
>. <TT
CLASS="LITERAL"
>FULL</TT
> records the old values of all columns
in the row. <TT
CLASS="LITERAL"
>NOTHING</TT
> 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.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>RENAME</TT
></DT
><DD
><P
> The <TT
CLASS="LITERAL"
>RENAME</TT
> 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.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET SCHEMA</TT
></DT
><DD
><P
> This form moves the table into another schema. Associated indexes,
constraints, and sequences owned by table columns are moved as well.
</P
></DD
></DL
></DIV
><P>
</P
><P
> All the forms of ALTER TABLE that act on a single table, except
<TT
CLASS="LITERAL"
>RENAME</TT
>, and <TT
CLASS="LITERAL"
>SET SCHEMA</TT
>
can be combined into a list of multiple alterations to applied together.
For example, it
is possible to add several columns and/or alter the type of several
columns in a single command. This is particularly useful with large
tables, since only one pass over the table need be made.
</P
><P
> You must own the table to use <TT
CLASS="COMMAND"
>ALTER TABLE</TT
>.
To change the schema or tablespace of a table, you must also have
<TT
CLASS="LITERAL"
>CREATE</TT
> 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 <TT
CLASS="LITERAL"
>CREATE</TT
> 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 <TT
CLASS="LITERAL"
>OF</TT
>
clause, you must also have <TT
CLASS="LITERAL"
>USAGE</TT
> privilege on the data
type.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN76398"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>IF EXISTS</TT
></DT
><DD
><P
> Do not throw an error if the table does not exist. A notice is issued
in this case.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
> The name (optionally schema-qualified) of an existing table to
alter. If <TT
CLASS="LITERAL"
>ONLY</TT
> is specified before the table name, only
that table is altered. If <TT
CLASS="LITERAL"
>ONLY</TT
> is not specified, the table
and all its descendant tables (if any) are altered. Optionally,
<TT
CLASS="LITERAL"
>*</TT
> can be specified after the table name to explicitly
indicate that descendant tables are included.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></DT
><DD
><P
> Name of a new or existing column.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>new_column_name</I
></TT
></DT
><DD
><P
> New name for an existing column.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>new_name</I
></TT
></DT
><DD
><P
> New name for the table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>data_type</I
></TT
></DT
><DD
><P
> Data type of the new column, or new data type for an existing
column.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>table_constraint</I
></TT
></DT
><DD
><P
> New table constraint for the table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
></DT
><DD
><P
> Name of a new or existing constraint.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CASCADE</TT
></DT
><DD
><P
> Automatically drop objects that depend on the dropped column
or constraint (for example, views referencing the column),
and in turn all objects that depend on those objects
(see <A
HREF="ddl-depend.html"
>Section 5.13</A
>).
</P
></DD
><DT
><TT
CLASS="LITERAL"
>RESTRICT</TT
></DT
><DD
><P
> Refuse to drop the column or constraint if there are any dependent
objects. This is the default behavior.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
></DT
><DD
><P
> Name of a single trigger to disable or enable.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>ALL</TT
></DT
><DD
><P
> 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.)
</P
></DD
><DT
><TT
CLASS="LITERAL"
>USER</TT
></DT
><DD
><P
> 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.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
></DT
><DD
><P
> The name of an existing index.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
></DT
><DD
><P
> The name of a table storage parameter.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
></DT
><DD
><P
> The new value for a table storage parameter.
This might be a number or a word depending on the parameter.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
></DT
><DD
><P
> A parent table to associate or de-associate with this table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>new_owner</I
></TT
></DT
><DD
><P
> The user name of the new owner of the table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>new_tablespace</I
></TT
></DT
><DD
><P
> The name of the tablespace to which the table will be moved.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>new_schema</I
></TT
></DT
><DD
><P
> The name of the schema to which the table will be moved.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-ALTERTABLE-NOTES"
></A
><H2
>Notes</H2
><P
> The key word <TT
CLASS="LITERAL"
>COLUMN</TT
> is noise and can be omitted.
</P
><P
> When a column is added with <TT
CLASS="LITERAL"
>ADD COLUMN</TT
>, all existing
rows in the table are initialized with the column's default value
(NULL if no <TT
CLASS="LITERAL"
>DEFAULT</TT
> clause is specified).
If there is no <TT
CLASS="LITERAL"
>DEFAULT</TT
> 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.
</P
><P
> Adding a column with a <TT
CLASS="LITERAL"
>DEFAULT</TT
> 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 <TT
CLASS="LITERAL"
>USING</TT
> 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 <TT
CLASS="LITERAL"
>oid</TT
> 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.
</P
><P
> Adding a <TT
CLASS="LITERAL"
>CHECK</TT
> or <TT
CLASS="LITERAL"
>NOT NULL</TT
> constraint requires
scanning the table to verify that existing rows meet the constraint,
but does not require a table rewrite.
</P
><P
> The main reason for providing the option to specify multiple changes
in a single <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> is that multiple table scans or
rewrites can thereby be combined into a single pass over the table.
</P
><P
> Scanning a large table to verify a new foreign key or check constraint
can take a long time, and other updates to the table are locked out
until the <TT
CLASS="COMMAND"
>ALTER TABLE ADD CONSTRAINT</TT
> command is
committed. The main purpose of the <TT
CLASS="LITERAL"
>NOT VALID</TT
>
constraint option is to reduce the impact of adding a constraint on
concurrent updates. With <TT
CLASS="LITERAL"
>NOT VALID</TT
>,
the <TT
CLASS="COMMAND"
>ADD CONSTRAINT</TT
> command does not scan the table
and can be committed immediately. After that, a <TT
CLASS="LITERAL"
>VALIDATE
CONSTRAINT</TT
> command can be issued to verify that existing rows
satisfy the constraint. The validation step does not need to lock out
concurrent updates, since it knows that other transactions will be
enforcing the constraint for rows that they insert or update; only
pre-existing rows need to be checked. Hence, validation acquires only
a <TT
CLASS="LITERAL"
>SHARE UPDATE EXCLUSIVE</TT
> lock on the table being
altered. (If the constraint is a foreign key then a <TT
CLASS="LITERAL"
>ROW
SHARE</TT
> lock is also required on the table referenced by the
constraint.) In addition to improving concurrency, it can be useful to
use <TT
CLASS="LITERAL"
>NOT VALID</TT
> and <TT
CLASS="LITERAL"
>VALIDATE
CONSTRAINT</TT
> in cases where the table is known to contain
pre-existing violations. Once the constraint is in place, no new
violations can be inserted, and the existing problems can be corrected
at leisure until <TT
CLASS="LITERAL"
>VALIDATE CONSTRAINT</TT
> finally
succeeds.
</P
><P
> The <TT
CLASS="LITERAL"
>DROP COLUMN</TT
> 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 <TT
CLASS="LITERAL"
>oid</TT
> column; that is done
with an immediate rewrite.)
</P
><P
> To force immediate reclamation of space occupied by a dropped column,
you can execute one of the forms of <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> that
performs a rewrite of the whole table. This results in reconstructing
each row with the dropped column replaced by a null value.
</P
><P
> The rewriting forms of <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> 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 <A
HREF="mvcc-caveats.html"
>Section 13.5</A
> for more details.
</P
><P
> The <TT
CLASS="LITERAL"
>USING</TT
> option of <TT
CLASS="LITERAL"
>SET DATA TYPE</TT
> 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 <TT
CLASS="LITERAL"
>SET DATA TYPE</TT
>
syntax. Because of this flexibility, the <TT
CLASS="LITERAL"
>USING</TT
>
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, <TT
CLASS="LITERAL"
>SET DATA TYPE</TT
> might fail to convert the default even
though a <TT
CLASS="LITERAL"
>USING</TT
> clause is supplied. In such cases,
drop the default with <TT
CLASS="LITERAL"
>DROP DEFAULT</TT
>, perform the <TT
CLASS="LITERAL"
>ALTER
TYPE</TT
>, and then use <TT
CLASS="LITERAL"
>SET DEFAULT</TT
> to add a suitable new
default. Similar considerations apply to indexes and constraints involving
the column.
</P
><P
> 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, <TT
CLASS="COMMAND"
>ALTER TABLE ONLY</TT
>
will be rejected. This ensures that the descendants always have
columns matching the parent.
</P
><P
> A recursive <TT
CLASS="LITERAL"
>DROP COLUMN</TT
> 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 <TT
CLASS="LITERAL"
>DROP
COLUMN</TT
> (i.e., <TT
CLASS="COMMAND"
>ALTER TABLE ONLY ... DROP
COLUMN</TT
>) never removes any descendant columns, but
instead marks them as independently defined rather than inherited.
</P
><P
> The <TT
CLASS="LITERAL"
>TRIGGER</TT
>, <TT
CLASS="LITERAL"
>CLUSTER</TT
>, <TT
CLASS="LITERAL"
>OWNER</TT
>,
and <TT
CLASS="LITERAL"
>TABLESPACE</TT
> actions never recurse to descendant tables;
that is, they always act as though <TT
CLASS="LITERAL"
>ONLY</TT
> were specified.
Adding a constraint recurses only for <TT
CLASS="LITERAL"
>CHECK</TT
> constraints
that are not marked <TT
CLASS="LITERAL"
>NO INHERIT</TT
>.
</P
><P
> Changing any part of a system catalog table is not permitted.
</P
><P
> Refer to <A
HREF="sql-createtable.html"
>CREATE TABLE</A
> for a further description of valid
parameters. <A
HREF="ddl.html"
>Chapter 5</A
> has further information on
inheritance.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN76569"
></A
><H2
>Examples</H2
><P
> To add a column of type <TT
CLASS="TYPE"
>varchar</TT
> to a table:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD COLUMN address varchar(30);</PRE
><P>
</P
><P
> To drop a column from a table:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors DROP COLUMN address RESTRICT;</PRE
><P>
</P
><P
> To change the types of two existing columns in one operation:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors
ALTER COLUMN address TYPE varchar(80),
ALTER COLUMN name TYPE varchar(100);</PRE
><P>
</P
><P
> To change an integer column containing Unix timestamps to <TT
CLASS="TYPE"
>timestamp
with time zone</TT
> via a <TT
CLASS="LITERAL"
>USING</TT
> clause:
</P><PRE
CLASS="PROGRAMLISTING"
>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';</PRE
><P>
</P
><P
> The same, when the column has a default expression that won't automatically
cast to the new data type:
</P><PRE
CLASS="PROGRAMLISTING"
>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();</PRE
><P>
</P
><P
> To rename an existing column:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors RENAME COLUMN address TO city;</PRE
><P>
</P
><P
> To rename an existing table:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors RENAME TO suppliers;</PRE
><P>
</P
><P
> To rename an existing constraint:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors RENAME CONSTRAINT zipchk TO zip_check;</PRE
><P>
</P
><P
> To add a not-null constraint to a column:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;</PRE
><P>
To remove a not-null constraint from a column:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;</PRE
><P>
</P
><P
> To add a check constraint to a table and all its children:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);</PRE
><P>
</P
><P
> To add a check constraint only to a table and not to its children:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5) NO INHERIT;</PRE
><P>
(The check constraint will not be inherited by future children, either.)
</P
><P
> To remove a check constraint from a table and all its children:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors DROP CONSTRAINT zipchk;</PRE
><P>
</P
><P
> To remove a check constraint from one table only:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE ONLY distributors DROP CONSTRAINT zipchk;</PRE
><P>
(The check constraint remains in place for any child tables.)
</P
><P
> To add a foreign key constraint to a table:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address);</PRE
><P>
</P
><P
> To add a foreign key constraint to a table with the least impact on other work:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) NOT VALID;
ALTER TABLE distributors VALIDATE CONSTRAINT distfk;</PRE
><P>
</P
><P
> To add a (multicolumn) unique constraint to a table:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);</PRE
><P>
</P
><P
> To add an automatically named primary key constraint to a table, noting
that a table can only ever have one primary key:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD PRIMARY KEY (dist_id);</PRE
><P>
</P
><P
> To move a table to a different tablespace:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors SET TABLESPACE fasttablespace;</PRE
><P>
</P
><P
> To move a table to a different schema:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE myschema.distributors SET SCHEMA yourschema;</PRE
><P>
</P
><P
> To recreate a primary key constraint, without blocking updates while the
index is rebuilt:
</P><PRE
CLASS="PROGRAMLISTING"
>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;</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN76615"
></A
><H2
>Compatibility</H2
><P
> The forms <TT
CLASS="LITERAL"
>ADD</TT
> (without <TT
CLASS="LITERAL"
>USING INDEX</TT
>),
<TT
CLASS="LITERAL"
>DROP</TT
>, <TT
CLASS="LITERAL"
>SET DEFAULT</TT
>,
and <TT
CLASS="LITERAL"
>SET DATA TYPE</TT
> (without <TT
CLASS="LITERAL"
>USING</TT
>)
conform with the SQL standard. The other forms are
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extensions of the SQL standard.
Also, the ability to specify more than one manipulation in a single
<TT
CLASS="COMMAND"
>ALTER TABLE</TT
> command is an extension.
</P
><P
> <TT
CLASS="COMMAND"
>ALTER TABLE DROP COLUMN</TT
> 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.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN76628"
></A
><H2
>See Also</H2
><A
HREF="sql-createtable.html"
>CREATE TABLE</A
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