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