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><H1
><A
NAME="SQL-ALTERTABLE"
></A
>ALTER TABLE</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN35231"
></A
><H2
>Name</H2
>ALTER TABLE -- change the definition of a table</DIV
><A
NAME="AEN35234"
></A
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN35236"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
ADD [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> <VAR
CLASS="REPLACEABLE"
>type</VAR
> [ <VAR
CLASS="REPLACEABLE"
>column_constraint</VAR
> [ ... ] ]
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
DROP [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> [ RESTRICT | CASCADE ]
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
ALTER [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> { SET DEFAULT <VAR
CLASS="REPLACEABLE"
>expression</VAR
> | DROP DEFAULT }
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
ALTER [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> { SET | DROP } NOT NULL
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
ALTER [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> SET STATISTICS <VAR
CLASS="REPLACEABLE"
>integer</VAR
>
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
ALTER [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
SET WITHOUT OIDS
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
RENAME [ COLUMN ] <VAR
CLASS="REPLACEABLE"
>column</VAR
> TO <VAR
CLASS="REPLACEABLE"
>new_column</VAR
>
ALTER TABLE <VAR
CLASS="REPLACEABLE"
>name</VAR
>
RENAME TO <VAR
CLASS="REPLACEABLE"
>new_name</VAR
>
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
ADD <VAR
CLASS="REPLACEABLE"
>table_constraint</VAR
>
ALTER TABLE [ ONLY ] <VAR
CLASS="REPLACEABLE"
>name</VAR
> [ * ]
DROP CONSTRAINT <VAR
CLASS="REPLACEABLE"
>constraint_name</VAR
> [ RESTRICT | CASCADE ]
ALTER TABLE <VAR
CLASS="REPLACEABLE"
>name</VAR
>
OWNER TO <VAR
CLASS="REPLACEABLE"
>new_owner</VAR
>
ALTER TABLE <VAR
CLASS="REPLACEABLE"
>name</VAR
>
CLUSTER ON <VAR
CLASS="REPLACEABLE"
>index_name</VAR
></PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN35268"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> changes the definition of an existing table.
There are several subforms:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>ADD COLUMN</TT
></DT
><DD
><P
> This form adds a new column to the table using the same syntax as
<A
HREF="sql-createtable.html"
><I
>CREATE TABLE</I
></A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DROP COLUMN</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.
</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.
The default values only apply to subsequent <TT
CLASS="COMMAND"
>INSERT</TT
>
commands; they do not cause rows already in the table to change.
Defaults may also be created for views, in which case they are
inserted into <TT
CLASS="COMMAND"
>INSERT</TT
> statements on the view before
the view's <TT
CLASS="LITERAL"
>ON INSERT</TT
> rule is applied.
</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"
><I
>ANALYZE</I
></A
> operations.
The target can be set in the range 0 to 1000; alternatively, set it
to -1 to revert to using the system default statistics target.
</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 supplementary 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 all
data types that support it. The use of <TT
CLASS="LITERAL"
>EXTERNAL</TT
> will, for example,
make substring operations on a <TT
CLASS="TYPE"
>text</TT
> column faster, at the penalty of
increased storage space.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>SET WITHOUT OIDS</TT
></DT
><DD
><P
> This form removes the <TT
CLASS="LITERAL"
>oid</TT
> column from the
table. Removing OIDs from a table does not occur immediately.
The space that the OID uses will be reclaimed when the row is
updated. Without updating the row, both the space and the value
of the OID are kept indefinitely. This is semantically similar
to the <TT
CLASS="LITERAL"
>DROP COLUMN</TT
> process.
</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, or view) or the name of an individual column in
a table. There is no effect on the stored data.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>ADD <VAR
CLASS="REPLACEABLE"
>table_constraint</VAR
></TT
></DT
><DD
><P
> This form adds a new constraint to a table using the same syntax as
<A
HREF="sql-createtable.html"
><I
>CREATE TABLE</I
></A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DROP CONSTRAINT</TT
></DT
><DD
><P
> This form drops constraints on a table.
Currently, constraints on tables are not required to have unique
names, so there may be more than one constraint matching the specified
name. All such constraints will be dropped.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>OWNER</TT
></DT
><DD
><P
> This form changes the owner of the table, index, sequence, or view to the
specified user.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CLUSTER</TT
></DT
><DD
><P
> This form marks a table for future <A
HREF="sql-cluster.html"
><I
>CLUSTER</I
></A
>
operations.
</P
></DD
></DL
></DIV
><P>
</P
><P
> You must own the table to use <TT
CLASS="COMMAND"
>ALTER TABLE</TT
>; except for
<TT
CLASS="COMMAND"
>ALTER TABLE OWNER</TT
>, which may only be executed by a superuser.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN35359"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><VAR
CLASS="REPLACEABLE"
>name</VAR
></DT
><DD
><P
> The name (possibly schema-qualified) of an existing table to
alter. If <TT
CLASS="LITERAL"
>ONLY</TT
> is specified, only that table is
altered. If <TT
CLASS="LITERAL"
>ONLY</TT
> is not specified, the table and all
its descendant tables (if any) are updated. <TT
CLASS="LITERAL"
>*</TT
> can be
appended to the table name to indicate that descendant tables are
to be altered, but in the current version, this is the default
behavior. (In releases before 7.1, <TT
CLASS="LITERAL"
>ONLY</TT
> was the
default behavior. The default can be altered by changing the
configuration parameter <VAR
CLASS="VARNAME"
>sql_inheritance</VAR
>.)
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>column</VAR
></DT
><DD
><P
> Name of a new or existing column.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>type</VAR
></DT
><DD
><P
> Data type of the new column.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>new_column</VAR
></DT
><DD
><P
> New name for an existing column.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>new_name</VAR
></DT
><DD
><P
> New name for the table.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>table_constraint</VAR
></DT
><DD
><P
> New table constraint for the table.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>constraint_name</VAR
></DT
><DD
><P
> Name of an existing constraint to drop.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>new_owner</VAR
></DT
><DD
><P
> The user name of the new owner of the table.
</P
></DD
><DT
><VAR
CLASS="REPLACEABLE"
>index_name</VAR
></DT
><DD
><P
> The index name on which the table should be marked for clustering.
</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).
</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
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN35422"
></A
><H2
>Notes</H2
><P
> The key word <TT
CLASS="LITERAL"
>COLUMN</TT
> is noise and can be omitted.
</P
><P
> In the current implementation of <TT
CLASS="LITERAL"
>ADD COLUMN</TT
>,
default and <TT
CLASS="LITERAL"
>NOT NULL</TT
> clauses for the new column are not supported.
The new column always comes into being with all values null.
You can use the <TT
CLASS="LITERAL"
>SET DEFAULT</TT
> form
of <TT
CLASS="COMMAND"
>ALTER TABLE</TT
> to set the default afterward.
(You may also want to update the already existing rows to the
new default value, using
<A
HREF="sql-update.html"
><I
>UPDATE</I
></A
>.)
If you want to mark the column non-null, use the <TT
CLASS="LITERAL"
>SET NOT NULL</TT
>
form after you've entered non-null values for the column in all rows.
</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.
To reclaim the space at once, do a dummy <TT
CLASS="COMMAND"
>UPDATE</TT
> of all rows
and then vacuum, as in:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE table SET col = col;
VACUUM FULL table;</PRE
><P>
</P
><P
> If a table has any descendant tables, it is not permitted to add
or rename a column 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
> Changing any part of a system catalog table is not permitted.
</P
><P
> Refer to <TT
CLASS="COMMAND"
>CREATE TABLE</TT
> 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="AEN35447"
></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 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 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:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);</PRE
><P>
</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 add a foreign key constraint to a table:
</P><PRE
CLASS="PROGRAMLISTING"
>ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) MATCH FULL;</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
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN35471"
></A
><H2
>Compatibility</H2
><P
> The <TT
CLASS="LITERAL"
>ADD COLUMN</TT
> form conforms with the SQL
standard, with the exception that it does not support defaults and
not-null constraints, as explained above. The <TT
CLASS="LITERAL"
>ALTER
COLUMN</TT
> form is in full conformance.
</P
><P
> The clauses to rename tables, columns, indexes, views, and sequences are
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extensions of the SQL standard.
</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
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