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Commit78ff6e0

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Doc: improve description of plpgsql's FETCH and MOVE commands.
We were not being clear about which variants of the "direction"clause are permitted in MOVE. Also, the text seemed to bewritten with only the FETCH/MOVE NEXT case in mind, so itdidn't apply very well to other variants.Also, document that "MOVE count IN cursor" only works if countis a constant. This is not the whole truth, because some othercases such as a parenthesized expression will also work, butwe want to push people to use "MOVE FORWARD count" instead.The constant case is enough to cover what we allow in plain SQL,and that seems sufficient to claim support for.Update a comment in pl_gram.y claiming that we don't documentthat point.Per gripe from Philipp Salvisberg.Discussion:https://postgr.es/m/172155553388.702.7932496598218792085@wrigleys.postgresql.org
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‎doc/src/sgml/plpgsql.sgml

Lines changed: 23 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -3230,13 +3230,16 @@ FETCH <optional> <replaceable>direction</replaceable> { FROM | IN } </optional>
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</synopsis>
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<para>
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<command>FETCH</command> retrieves the next row from the
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<command>FETCH</command> retrieves the next row (in the indicated
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direction) from the
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cursor into a target, which might be a row variable, a record
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variable, or a comma-separated list of simple variables, just like
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<command>SELECT INTO</command>. If there is nonext row, the
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<command>SELECT INTO</command>. If there is nosuitable row, the
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target is set to NULL(s). As with <command>SELECT
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INTO</command>, the special variable <literal>FOUND</literal> can
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be checked to see whether a row was obtained or not.
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be checked to see whether a row was obtained or not. If no row is
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obtained, the cursor is positioned after the last row or before the
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first row, depending on the movement direction.
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</para>
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<para>
@@ -3288,11 +3291,25 @@ MOVE <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <
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<para>
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<command>MOVE</command> repositions a cursor without retrieving
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any data. <command>MOVE</command> worksexactlylike the
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any data. <command>MOVE</command> works like the
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<command>FETCH</command> command, except it only repositions the
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cursor and does not return the row moved to. As with <command>SELECT
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cursor and does not return the row moved to.
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The <replaceable>direction</replaceable> clause can be any of the
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variants allowed in the SQL <xref linkend="sql-fetch"/>
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command, including those that can fetch more than one row;
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the cursor is positioned to the last such row.
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(However, the case in which the <replaceable>direction</replaceable>
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clause is simply a <replaceable>count</replaceable> expression with
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no key word is deprecated in <application>PL/pgSQL</application>.
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That syntax is ambiguous with the case where
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the <replaceable>direction</replaceable> clause is omitted
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altogether, and hence it may fail if
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the <replaceable>count</replaceable> is not a constant.)
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As with <command>SELECT
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INTO</command>, the special variable <literal>FOUND</literal> can
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be checked to see whether there was a next row to move to.
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be checked to see whether there was a row to move to. If there is no
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such row, the cursor is positioned after the last row or before the
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first row, depending on the movement direction.
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</para>
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<para>

‎src/pl/plpgsql/src/pl_gram.y

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -3150,11 +3150,11 @@ read_fetch_direction(void)
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{
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/*
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* Assume it's a count expression with no preceding keyword.
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* Note: we allow this syntax because core SQL does, butwe don't
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*document it because oftheambiguity with the omitted-direction
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*case. Forinstance, "MOVE n IN c" will fail if n is a variable.
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*Perhaps this can be improved someday, but it's hardly worth a
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* lot of work.
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* Note: we allow this syntax because core SQL does, butit's
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*ambiguous withthecase of an omitteddirection clause; for
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* instance, "MOVE n IN c" will fail if n is a variable, because the
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*preceding else-arm will trigger. Perhaps this can be improved
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*someday, but it hardly seems worth alot of work.
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*/
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plpgsql_push_back_token(tok);
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fetch->expr = read_sql_expression2(K_FROM, K_IN,

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