ALTER TABLE rewrite. New cool stuff:

* ALTER ... ADD COLUMN with defaults and NOT NULL constraints works per SQL
spec.  A default is implemented by rewriting the table with the new value
stored in each row.

* ALTER COLUMN TYPE.  You can change a column's datatype to anything you
want, so long as you can specify how to convert the old value.  Rewrites
the table.  (Possible future improvement: optimize no-op conversions such
as varchar(N) to varchar(N+1).)

* Multiple ALTER actions in a single ALTER TABLE command.  You can perform
any number of column additions, type changes, and constraint additions with
only one pass over the table contents.

Basic documentation provided in ALTER TABLE ref page, but some more docs
work is needed.

Original patch from Rod Taylor, additional work from Tom Lane.

Author: tglsfdc

doc/src/sgml/ref/alter_table.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.68 2004/03/24 09:49:20 neilc Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.69 2004/05/05 04:48:45 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -21,31 +21,26 @@ PostgreSQL documentation
  <refsynopsisdiv>
 <synopsis>
 ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
-    ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable> [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
+    <replaceable class="PARAMETER">action</replaceable> [, ... ]
 ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
+    RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable class="PARAMETER">new_column</replaceable>
+ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
+    RENAME TO <replaceable class="PARAMETER">new_name</replaceable>
+
+where <replaceable class="PARAMETER">action</replaceable> is one of:
+
+    ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable> [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
     DROP [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> [ RESTRICT | CASCADE ]
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
-    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET DEFAULT <replaceable class="PARAMETER">expression</replaceable> | DROP DEFAULT }
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
+    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TYPE <replaceable class="PARAMETER">type</replaceable> [ USING <replaceable class="PARAMETER">expression</replaceable> ]
+    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET DEFAULT <replaceable class="PARAMETER">expression</replaceable>
+    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> DROP DEFAULT
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET | DROP } NOT NULL
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STATISTICS <replaceable class="PARAMETER">integer</replaceable>
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
-    SET WITHOUT OIDS
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
-    RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable
-    class="PARAMETER">new_column</replaceable>
-ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
-    RENAME TO <replaceable class="PARAMETER">new_name</replaceable>
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
     ADD <replaceable class="PARAMETER">table_constraint</replaceable>
-ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
     DROP CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
-ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
+    SET WITHOUT OIDS
     OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
-ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
     CLUSTER ON <replaceable class="PARAMETER">index_name</replaceable>
 </synopsis>
  </refsynopsisdiv>
@@ -81,6 +76,23 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>ALTER COLUMN TYPE</literal></term>
+    <listitem>
+     <para>
+      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 <literal>USING</literal>
+      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  <literal>USING</literal>
+      clause must be provided if there is no implicit or assignment
+      cast from old to new type.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>SET</literal>/<literal>DROP DEFAULT</literal></term>
     <listitem>
@@ -147,53 +159,42 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
    </varlistentry>
 
    <varlistentry>
-    <term><literal>SET WITHOUT OIDS</literal></term>
+    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable></literal></term>
     <listitem>
      <para>
-      This form removes the <literal>oid</literal> system column from the
-      table.  This is exactly equivalent to
-      <literal>DROP COLUMN oid RESTRICT</literal>,
-      except that it will not complain if there is already no
-      <literal>oid</literal> column.
-     </para>
-
-     <para>
-      Note that there is no variant of <command>ALTER TABLE</command>
-      that allows OIDs to be restored to a table once they have been
-      removed.
+      This form adds a new constraint to a table using the same syntax as
+      <xref linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-TITLE">. 
      </para>
     </listitem>
    </varlistentry>
 
    <varlistentry>
-    <term><literal>RENAME</literal></term>
+    <term><literal>DROP CONSTRAINT</literal></term>
     <listitem>
      <para>
-      The <literal>RENAME</literal> 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.
+      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 matching constraints will be dropped.
      </para>
     </listitem>
    </varlistentry>
 
    <varlistentry>
-    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable></literal></term>
+    <term><literal>SET WITHOUT OIDS</literal></term>
     <listitem>
      <para>
-      This form adds a new constraint to a table using the same syntax as
-      <xref linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-TITLE">. 
+      This form removes the <literal>oid</literal> system column from the
+      table.  This is exactly equivalent to
+      <literal>DROP COLUMN oid RESTRICT</literal>,
+      except that it will not complain if there is already no
+      <literal>oid</literal> column.
      </para>
-    </listitem>
-   </varlistentry>
 
-   <varlistentry>
-    <term><literal>DROP CONSTRAINT</literal></term>
-    <listitem>
      <para>
-      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.
+      Note that there is no variant of <command>ALTER TABLE</command>
+      that allows OIDs to be restored to a table once they have been
+      removed.
      </para>
     </listitem>
    </varlistentry>
@@ -212,15 +213,34 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
     <term><literal>CLUSTER</literal></term>
     <listitem>
      <para>
-      This form marks a table for future <xref linkend="SQL-CLUSTER" endterm="sql-cluster-title">
+      This form selects the default controlling index for future <xref linkend="SQL-CLUSTER" endterm="sql-cluster-title">
       operations.
      </para>
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>RENAME</literal></term>
+    <listitem>
+     <para>
+      The <literal>RENAME</literal> 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.
+     </para>
+    </listitem>
+   </varlistentry>
+
   </variablelist>
   </para>
 
+  <para>
+   All the actions except <literal>RENAME</literal> 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.
+  </para>
+
   <para>
    You must own the table to use <command>ALTER TABLE</>; except for
    <command>ALTER TABLE OWNER</>, which may only be executed by a superuser.
@@ -262,7 +282,8 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
       <term><replaceable class="PARAMETER">type</replaceable></term>
       <listitem>
        <para>
-	Data type of the new column.
+	Data type of the new column, or new data type for an existing
+	column.
        </para>
       </listitem>
      </varlistentry>
@@ -352,16 +373,27 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
    </para>
 
    <para>
-    In the current implementation of <literal>ADD COLUMN</literal>,
-    default and <literal>NOT NULL</> clauses for the new column are not supported.
-    The new column always comes into being with all values null.
-    You can use the <literal>SET DEFAULT</literal> form
-    of <command>ALTER TABLE</command> to set the default afterward.
-    (You may also want to update the already existing rows to the
-    new default value, using
-    <xref linkend="sql-update" endterm="sql-update-title">.)
-    If you want to mark the column non-null, use the <literal>SET NOT NULL</>
-    form after you've entered non-null values for the column in all rows.
+    When a column is added with <literal>ADD COLUMN</literal>, all existing
+    rows in the table are initialized with the column's default value
+    (NULL if no <literal>DEFAULT</> clause is specified).
+   </para>
+
+   <para>
+    Adding a column with a non-null default or changing the type of an
+    existing column will require the entire table to be rewritten.  This
+    may take a significant amount of time for a large table; and it will
+    temporarily require double the disk space.
+   </para>
+
+   <para>
+    Adding a <literal>CHECK</> or <literal>NOT NULL</> constraint requires
+    scanning the table to verify that existing rows meet the constraint.
+   </para>
+
+   <para>
+    The main reason for providing the option to specify multiple changes
+    in a single <command>ALTER TABLE</> is that multiple table scans or
+    rewrites can thereby be combined into a single pass over the table.
    </para>
 
    <para>
@@ -381,9 +413,9 @@ VACUUM FULL table;
    </para>
 
    <para>
-    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, <command>ALTER TABLE ONLY</command>
+    If a table has any descendant tables, it is not permitted to add,
+    rename, or change the type of a column in the parent table without doing
+    the same to the descendants.  That is, <command>ALTER TABLE ONLY</command>
     will be rejected.  This ensures that the descendants always have
     columns matching the parent.
    </para>
@@ -427,6 +459,15 @@ ALTER TABLE distributors DROP COLUMN address RESTRICT;
 </programlisting>
   </para>
 
+  <para>
+   To change the types of two existing columns in one operation:
+<programlisting>
+ALTER TABLE distributors
+    ALTER COLUMN address TYPE varchar(80),
+    ALTER COLUMN name TYPE varchar(100);
+</programlisting>
+  </para>
+
   <para>
    To rename an existing column:
 <programlisting>
@@ -493,15 +534,11 @@ ALTER TABLE distributors ADD PRIMARY KEY (dist_id);
   <title>Compatibility</title>
 
   <para>
-   The <literal>ADD COLUMN</literal> form conforms with the SQL
-   standard, with the exception that it does not support defaults and
-   not-null constraints, as explained above.  The <literal>ALTER
-   COLUMN</literal> form is in full conformance.
-  </para>
-
-  <para>
-   The clauses to rename tables, columns, indexes, views, and sequences are
+   The <literal>ADD</literal>, <literal>DROP</>, and <literal>SET DEFAULT</>
+   forms conform with the SQL standard.  The other forms are
    <productname>PostgreSQL</productname> extensions of the SQL standard.
+   Also, the ability to specify more than one manipulation in a single
+   <command>ALTER TABLE</> command is an extension.
   </para>
 
   <para>

src/backend/bootstrap/bootparse.y

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/bootstrap/bootparse.y,v 1.65 2004/03/23 19:35:16 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/bootstrap/bootparse.y,v 1.66 2004/05/05 04:48:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -241,7 +241,9 @@ Boot_DeclareIndexStmt:
 								LexIDStr($3),
 								LexIDStr($7),
 								$9,
-								false, false, false, NULL, NIL);
+								NULL, NIL,
+								false, false, false,
+								false, false, true, false);
 					do_end();
 				}
 		;
@@ -255,7 +257,9 @@ Boot_DeclareUniqueIndexStmt:
 								LexIDStr($4),
 								LexIDStr($8),
 								$10,
-								true, false, false, NULL, NIL);
+								NULL, NIL,
+								true, false, false,
+								false, false, true, false);
 					do_end();
 				}
 		;