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Drop the rule against included index columns duplicating key columns.

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The initial version of the included-index-column feature stated that
included columns couldn't be the same as any key column of the index.
While it'd be pretty silly to do that, since the included column would be
entirely redundant, we've never prohibited redundant index columns before
so it's not very consistent to do so here.  Moreover, the prohibition
was itself badly implemented, so that it failed to reject columns that
were effectively identical but not spelled quite alike, as reported by
Aditya Toshniwal.

(Moreover, it's not hard to imagine that for some non-btree index types,
such cases would be non-silly anyhow: the index might use a lossy
representation for key columns but be able to support retrieval of the
original form of included columns.)

Hence, let's just drop the prohibition.

In passing, do some copy-editing on the documentation for the
included-column feature.

Yugo Nagata; documentation and test corrections by me

Discussion: https://postgr.es/m/CAM9w-_mhBCys4fQNfaiQKTRrVWtoFrZ-wXmDuE9Nj5y-Y7aDKQ@mail.gmail.com
This commit is contained in:
Tom Lane
2018-07-18 14:43:03 -04:00
parent 3cb646264e
commit 701fd0bbc9
8 changed files with 58 additions and 64 deletions
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10
doc/src/sgml/ref/create_table.sgml
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@@ -869,9 +869,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
one or more columns on which the uniqueness is not enforced.
Note that although the constraint is not enforced on the included columns,
it still depends on them. Consequently, some operations on these columns
(e.g. <literal>DROP COLUMN</literal>) can cause cascade constraint and
index deletion. See paragraph about <literal>INCLUDE</literal> in
<xref linkend="sql-createindex"/> for more information.
(e.g. <literal>DROP COLUMN</literal>) can cause cascaded constraint and
index deletion.
</para>
</listitem>
</varlistentry>
@@ -916,9 +915,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
of columns to be specified which will be included in the non-key portion
of the index. Although uniqueness is not enforced on the included columns,
the constraint still depends on them. Consequently, some operations on the
included columns (e.g. <literal>DROP COLUMN</literal>) can cause cascade
constraint and index deletion. See paragraph about <literal>INCLUDE</literal>
in <xref linkend="sql-createindex"/> for more information.
included columns (e.g. <literal>DROP COLUMN</literal>) can cause cascaded
constraint and index deletion.
</para>
</listitem>
</varlistentry>