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Commitdd979f6

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Redesign DISTINCT ON as discussed in pgsql-sql 1/25/00: syntax is now
SELECT DISTINCT ON (expr [, expr ...]) targetlist ...and there is a check to make sure that the user didn't specify an ORDER BYthat's incompatible with the DISTINCT operation.Reimplement nodeUnique and nodeGroup to use the proper datatype-specificequality function for each column being compared --- they used to dobitwise comparisons or convert the data to text strings and strcmp().(To add insult to injury, they'd look up the conversion functions oncefor each tuple...) Parse/plan representation of DISTINCT is now a listof SortClause nodes.initdb forced by querytree change...
1 parent3f0074e commitdd979f6

32 files changed

+607
-545
lines changed

‎doc/src/sgml/ref/select.sgml

Lines changed: 21 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.23 1999/12/13 17:39:38 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.24 2000/01/27 18:11:25 tgl Exp $
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Postgres documentation
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-->
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@@ -22,7 +22,7 @@ Postgres documentation
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<date>1999-07-20</date>
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</refsynopsisdivinfo>
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<synopsis>
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SELECT [ ALL | DISTINCT [ ON <replaceable class="PARAMETER">column</replaceable> ] ]
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SELECT [ ALL | DISTINCT [ ON(<replaceable class="PARAMETER">expression</replaceable> [, ...] ) ] ]
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<replaceable class="PARAMETER">expression</replaceable> [ AS <replaceable class="PARAMETER">name</replaceable> ] [, ...]
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[ INTO [ TEMPORARY | TEMP ] [ TABLE ] <replaceable class="PARAMETER">new_table</replaceable> ]
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[ FROM <replaceable class="PARAMETER">table</replaceable> [ <replaceable class="PARAMETER">alias</replaceable> ] [, ...] ]
@@ -201,16 +201,29 @@ SELECT [ ALL | DISTINCT [ ON <replaceable class="PARAMETER">column</replaceable>
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</para>
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<para>
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<command>DISTINCT</command> will eliminateallduplicate rows from the
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<command>DISTINCT</command> will eliminate duplicate rows from the
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result.
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<command>DISTINCT ON <replaceable class="PARAMETER">column</replaceable></command>
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will eliminate all duplicates in the specified column; this is
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similar to using
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<command>GROUP BY <replaceable class="PARAMETER">column</replaceable></command>.
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<command>ALL</command> will return all candidate rows,
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<command>ALL</command> (the default) will return all candidate rows,
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including duplicates.
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</para>
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<para>
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<command>DISTINCT ON</command> eliminates rows that match on all the
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specified expressions, keeping only the first row of each set of
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duplicates. Note that "the first row" of each set is unpredictable
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unless <command>ORDER BY</command> is used to ensure that the desired
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row appears first. For example,
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<programlisting>
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SELECT DISTINCT ON (location) location, time, report
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FROM weatherReports
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ORDER BY location, time DESC;
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</programlisting>
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retrieves the most recent weather report for each location. But if
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we had not used ORDER BY to force descending order of time values
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for each location, we'd have gotten a report of unpredictable age
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for each location.
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</para>
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<para>
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The GROUP BY clause allows a user to divide a table
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conceptually into groups.

‎src/backend/executor/execTuples.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/executor/execTuples.c,v 1.35 2000/01/26 05:56:22 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/executor/execTuples.c,v 1.36 2000/01/27 18:11:27 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -753,7 +753,7 @@ NodeGetResultTupleSlot(Plan *node)
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{
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UniqueState*uniquestate= ((Unique*)node)->uniquestate;
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slot=uniquestate->cs_ResultTupleSlot;
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slot=uniquestate->cstate.cs_ResultTupleSlot;
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}
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break;
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