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doc/man/alter_table.l

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+.\" This is -*-nroff-*-
+.\" XXX standard disclaimer belongs here....
+.\" $Header: /cvsroot/pgsql/doc/man/Attic/alter_table.l,v 1.1.1.1 1996/08/18 22:14:19 scrappy Exp $
+.TH "ALTER TABLE" SQL 11/5/95 Postgres95 Postgres95
+.SH NAME
+alter table \(em add attributes to a class
+.SH SYNOPSIS
+.nf
+\fBalter table\fR classname [*]
+	\fBadd column\fR attname type
+	
+.fi
+.SH DESCRIPTION
+The
+.BR "alter table"
+command
+causes a new attribute to be added to an existing class,
+.IR classname .
+The new attributes and their types are specified
+in the same style and with the the same restrictions as in
+.IR create table (l).
+.PP
+In order to add an attribute to each class in an entire inheritance
+hierarchy, use the
+.IR classname
+of the superclass and append a \*(lq*\*(rq.  (By default, the
+attribute will not be added to any of the subclasses.)  This should
+.BR always
+be done when adding an attribute to a superclass.  If it is not,
+queries on the inheritance hierarchy such as
+.nf
+select * from super* s
+.fi
+will not work because the subclasses will be missing an attribute
+found in the superclass.
+.PP
+For efficiency reasons, default values for added attributes are not
+placed in existing instances of a class.  That is, existing instances
+will have NULL values in the new attributes.  If non-NULL values are
+desired, a subsequent
+.IR update (l)
+query should be run.
+.PP
+You must own the class in order to change its schema.
+.SH EXAMPLE
+.nf
+--
+-- add the date of hire to the emp class
+-- 
+alter table emp add column hiredate abstime
+.fi
+.nf
+--
+-- add a health-care number to all persons
+-- (including employees, students, ...)
+--
+alter table person * add column health_care_id int4
+.fi
+.SH "SEE ALSO"
+create table (l),
+update (l).