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Support FETCH FIRST WITH TIES

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WITH TIES is an option to the FETCH FIRST N ROWS clause (the SQL
standard's spelling of LIMIT), where you additionally get rows that
compare equal to the last of those N rows by the columns in the
mandatory ORDER BY clause.

There was a proposal by Andrew Gierth to implement this functionality in
a more powerful way that would yield more features, but the other patch
had not been finished at this time, so we decided to use this one for
now in the spirit of incremental development.

Author: Surafel Temesgen <surafel3000@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Discussion: https://postgr.es/m/CALAY4q9ky7rD_A4vf=FVQvCGngm3LOes-ky0J6euMrg=_Se+ag@mail.gmail.com
Discussion: https://postgr.es/m/87o8wvz253.fsf@news-spur.riddles.org.uk
This commit is contained in:
Alvaro Herrera
2020-04-07 16:22:13 -04:00
parent 26a944cf29
commit 357889eb17
25 changed files with 616 additions and 75 deletions
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27
src/backend/utils/adt/ruleutils.c
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@ -5243,7 +5243,10 @@ get_select_query_def(Query *query, deparse_context *context,
force_colno, context);
}
/* Add the LIMIT clause if given */
/*
* Add the LIMIT/OFFSET clauses if given. If non-default options, use the
* standard spelling of LIMIT.
*/
if (query->limitOffset != NULL)
{
appendContextKeyword(context, " OFFSET ",
@ -5252,13 +5255,23 @@ get_select_query_def(Query *query, deparse_context *context,
}
if (query->limitCount != NULL)
{
appendContextKeyword(context, " LIMIT ",
-PRETTYINDENT_STD, PRETTYINDENT_STD, 0);
if (IsA(query->limitCount, Const) &&
((Const *) query->limitCount)->constisnull)
appendStringInfoString(buf, "ALL");
else
if (query->limitOption == LIMIT_OPTION_WITH_TIES)
{
appendContextKeyword(context, " FETCH FIRST ",
-PRETTYINDENT_STD, PRETTYINDENT_STD, 0);
get_rule_expr(query->limitCount, context, false);
appendStringInfo(buf, " ROWS WITH TIES");
}
else
{
appendContextKeyword(context, " LIMIT ",
-PRETTYINDENT_STD, PRETTYINDENT_STD, 0);
if (IsA(query->limitCount, Const) &&
((Const *) query->limitCount)->constisnull)
appendStringInfoString(buf, "ALL");
else
get_rule_expr(query->limitCount, context, false);
}
}
/* Add FOR [KEY] UPDATE/SHARE clauses if present */