NotificationsYou must be signed in to change notification settings
Fork28
Star151

Commitdd979f6

committed

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 commitdd979f6Copy full SHA for dd979f6

File tree

32 files changed

+607

-545

lines changed

doc/src/sgml/ref
- select.sgml
src
- backend
  - executor
  - nodes
  - optimizer
    - plan
      - createplan.c
      - planner.c
    - prep
      - prepkeyset.c
      - prepunion.c
    - util
      - tlist.c
  - parser
  - rewrite
- include
  - catalog
    - catversion.h
  - executor
    - nodeGroup.h
  - nodes
  - optimizer
    - planmain.h
    - tlist.h
  - parser
    - parse_clause.h
- test/regress
  - expected
    - errors.out
    - select_distinct_on.out
  - sql
    - errors.sql
    - select_distinct_on.sql

32 files changed

+607

-545

lines changed

`‎doc/src/sgml/ref/select.sgml‎`

Lines changed: 21 additions & 8 deletions

Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,5 @@`
`1`	`1`	`<!--`
`2`		`-$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.23 1999/12/13 17:39:38 tgl Exp $`
	`2`	`+$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.24 2000/01/27 18:11:25 tgl Exp $`
`3`	`3`	`Postgres documentation`
`4`	`4`	`-->`
`5`	`5`
`@@ -22,7 +22,7 @@ Postgres documentation`
`22`	`22`	`<date>1999-07-20</date>`
`23`	`23`	`</refsynopsisdivinfo>`
`24`	`24`	`<synopsis>`
`25`		`-SELECT [ ALL \| DISTINCT [ ON <replaceable class="PARAMETER">column</replaceable> ] ]`
	`25`	`+SELECT [ ALL \| DISTINCT [ ON(<replaceable class="PARAMETER">expression</replaceable> [, ...] ) ] ]`
`26`	`26`	`<replaceable class="PARAMETER">expression</replaceable> [ AS <replaceable class="PARAMETER">name</replaceable> ] [, ...]`
`27`	`27`	`[ INTO [ TEMPORARY \| TEMP ] [ TABLE ] <replaceable class="PARAMETER">new_table</replaceable> ]`
`28`	`28`	`[ FROM <replaceable class="PARAMETER">table</replaceable> [ <replaceable class="PARAMETER">alias</replaceable> ] [, ...] ]`
`@@ -201,16 +201,29 @@ SELECT [ ALL \| DISTINCT [ ON <replaceable class="PARAMETER">column</replaceable>`
`201`	`201`	`</para>`
`202`	`202`
`203`	`203`	`<para>`
`204`		`- <command>DISTINCT</command> will eliminateallduplicate rows from the`
	`204`	`+ <command>DISTINCT</command> will eliminate duplicate rows from the`
`205`	`205`	`result.`
`206`		`- <command>DISTINCT ON <replaceable class="PARAMETER">column</replaceable></command>`
`207`		`- will eliminate all duplicates in the specified column; this is`
`208`		`- similar to using`
`209`		`- <command>GROUP BY <replaceable class="PARAMETER">column</replaceable></command>.`
`210`		`- <command>ALL</command> will return all candidate rows,`
	`206`	`+ <command>ALL</command> (the default) will return all candidate rows,`
`211`	`207`	`including duplicates.`
`212`	`208`	`</para>`
`213`	`209`
	`210`	`+ <para>`
	`211`	`+ <command>DISTINCT ON</command> eliminates rows that match on all the`
	`212`	`+ specified expressions, keeping only the first row of each set of`
	`213`	`+ duplicates. Note that "the first row" of each set is unpredictable`
	`214`	`+ unless <command>ORDER BY</command> is used to ensure that the desired`
	`215`	`+ row appears first. For example,`
	`216`	`+ <programlisting>`
	`217`	`+ SELECT DISTINCT ON (location) location, time, report`
	`218`	`+ FROM weatherReports`
	`219`	`+ ORDER BY location, time DESC;`
	`220`	`+ </programlisting>`
	`221`	`+ retrieves the most recent weather report for each location. But if`
	`222`	`+ we had not used ORDER BY to force descending order of time values`
	`223`	`+ for each location, we'd have gotten a report of unpredictable age`
	`224`	`+ for each location.`
	`225`	`+ </para>`
	`226`	`+`
`214`	`227`	`<para>`
`215`	`228`	`The GROUP BY clause allows a user to divide a table`
`216`	`229`	`conceptually into groups.`

`‎src/backend/executor/execTuples.c‎`

Lines changed: 2 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -15,7 +15,7 @@`
`15`	`15`	`*`
`16`	`16`	`*`
`17`	`17`	`* IDENTIFICATION`
`18`		`- * $Header: /cvsroot/pgsql/src/backend/executor/execTuples.c,v 1.35 2000/01/26 05:56:22 momjian Exp $`
	`18`	`+ * $Header: /cvsroot/pgsql/src/backend/executor/execTuples.c,v 1.36 2000/01/27 18:11:27 tgl Exp $`
`19`	`19`	`*`
`20`	`20`	`*-------------------------------------------------------------------------`
`21`	`21`	`*/`
`@@ -753,7 +753,7 @@ NodeGetResultTupleSlot(Plan *node)`
`753`	`753`	`{`
`754`	`754`	`UniqueStateuniquestate= ((Unique)node)->uniquestate;`
`755`	`755`
`756`		`-slot=uniquestate->cs_ResultTupleSlot;`
	`756`	`+slot=uniquestate->cstate.cs_ResultTupleSlot;`
`757`	`757`	`}`
`758`	`758`	`break;`
`759`	`759`

0 commit comments

Comments

(0)

Movatterモバイル変換

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commitdd979f6

File tree

32 files changed

32 files changed

`‎doc/src/sgml/ref/select.sgml‎`

`‎src/backend/executor/execTuples.c‎`

0 commit comments