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<para>

<command>ALTER TABLE</command> changes the definition of an existing table.

The <literal>ADD COLUMN</literal> form adds a new column to the table

The <literal>ALTER COLUMN SET/DROP DEFAULT</literal> forms

allow you to set or remove the default for the column. Note that defaults

only apply to subsequent <command>INSERT</command> commands; they do not

cause rows already in the table to change.

The <literal>ALTER COLUMN SET STATISTICS</literal> form allows you to

set the statistics-gathering target for subsequent

The <literal>RENAME</literal> clause causes the name of a table or column

to change without changing any of the data contained in

the affected table. Thus, the table or column will

remain of the same type and size after this command is

executed.

The ADD <replaceable class="PARAMETER">table constraint definition</replaceable> clause

adds a new constraint to the table using the same syntax as <xref

The DROP CONSTRAINT <replaceable class="PARAMETER">constraint</replaceable> clause

drops all CHECK constraints on the table (and its children) that match <replaceable class="PARAMETER">constraint</replaceable>.

The OWNER clause changes the owner of the table to the user <replaceable class="PARAMETER">

You can use the <literal>SET DEFAULT</literal> form

of <command>ALTER TABLE</command> to set the default later.

(You may also want to update the already existing rows to the

</para>

<para>

Currently only CHECK constraints can be dropped from a table. The RESTRICT

keyword is required, although dependencies are not checked. The CASCADE

option is unsupported. To remove a PRIMARY or UNIQUE constraint, drop the

To remove FOREIGN KEY constraints you need to recreate

and reload the table, using other parameters to the

command.

</para>

<para>