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Allow an alias to be attached to a JOIN ... USING

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This allows something like

    SELECT ... FROM t1 JOIN t2 USING (a, b, c) AS x

where x has the columns a, b, c and unlike a regular alias it does not
hide the range variables of the tables being joined t1 and t2.

Per SQL:2016 feature F404 "Range variable for common column names".

Reviewed-by: Vik Fearing <vik.fearing@2ndquadrant.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/454638cf-d563-ab76-a585-2564428062af@2ndquadrant.com
This commit is contained in:
Peter Eisentraut
2021-03-31 17:09:24 +02:00
parent 27e1f14563
commit 055fee7eb4
22 changed files with 315 additions and 29 deletions
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32
src/backend/parser/parse_clause.c
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@ -1265,6 +1265,13 @@ transformFromClauseItem(ParseState *pstate, Node *n,
j->usingClause = rlist;
}
/*
* If a USING clause alias was specified, save the USING columns as
* its column list.
*/
if (j->join_using_alias)
j->join_using_alias->colnames = j->usingClause;
/*
* Now transform the join qualifications, if any.
*/
@ -1460,6 +1467,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
res_colvars,
l_colnos,
r_colnos,
j->join_using_alias,
j->alias,
true);
@ -1493,6 +1501,30 @@ transformFromClauseItem(ParseState *pstate, Node *n,
pstate->p_joinexprs = lappend(pstate->p_joinexprs, j);
Assert(list_length(pstate->p_joinexprs) == j->rtindex);
/*
* If the join has a USING alias, build a ParseNamespaceItem for that
* and add it to the list of nsitems in the join's input.
*/
if (j->join_using_alias)
{
ParseNamespaceItem *jnsitem;
jnsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
jnsitem->p_names = j->join_using_alias;
jnsitem->p_rte = nsitem->p_rte;
jnsitem->p_rtindex = nsitem->p_rtindex;
/* no need to copy the first N columns, just use res_nscolumns */
jnsitem->p_nscolumns = res_nscolumns;
/* set default visibility flags; might get changed later */
jnsitem->p_rel_visible = true;
jnsitem->p_cols_visible = true;
jnsitem->p_lateral_only = false;
jnsitem->p_lateral_ok = true;
/* Per SQL, we must check for alias conflicts */
checkNameSpaceConflicts(pstate, list_make1(jnsitem), my_namespace);
my_namespace = lappend(my_namespace, jnsitem);
}
/*
* Prepare returned namespace list. If the JOIN has an alias then it
* hides the contained RTEs completely; otherwise, the contained RTEs