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Allow empty target list in SELECT.

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This fixes a problem noted as a followup to bug #8648: if a query has a
semantically-empty target list, e.g. SELECT * FROM zero_column_table,
ruleutils.c will dump it as a syntactically-empty target list, which was
not allowed.  There doesn't seem to be any reliable way to fix this by
hacking ruleutils (note in particular that the originally zero-column table
might since have had columns added to it); and even if we had such a fix,
it would do nothing for existing dump files that might contain bad syntax.
The best bet seems to be to relax the syntactic restriction.

Also, add parse-analysis errors for SELECT DISTINCT with no columns (after
*-expansion) and RETURNING with no columns.  These cases previously
produced unexpected behavior because the parsed Query looked like it had
no DISTINCT or RETURNING clause, respectively.  If anyone ever offers
a plausible use-case for this, we could work a bit harder on making the
situation distinguishable.

Arguably this is a bug fix that should be back-patched, but I'm worried
that there may be client apps or PLs that expect "SELECT ;" to throw a
syntax error.  The issue doesn't seem important enough to risk changing
behavior in minor releases.
This commit is contained in:
Tom Lane
2013-12-14 20:23:26 -05:00
parent c03ad5602f
commit 1b4f7f93b4
6 changed files with 73 additions and 33 deletions
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13
src/backend/parser/analyze.c
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@@ -2018,6 +2018,19 @@ transformReturningList(ParseState *pstate, List *returningList)
/* transform RETURNING identically to a SELECT targetlist */
rlist = transformTargetList(pstate, returningList, EXPR_KIND_RETURNING);
/*
* Complain if the nonempty tlist expanded to nothing (which is possible
* if it contains only a star-expansion of a zero-column table). If we
* allow this, the parsed Query will look like it didn't have RETURNING,
* with results that would probably surprise the user.
*/
if (rlist == NIL)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("RETURNING must have at least one column"),
parser_errposition(pstate,
exprLocation(linitial(returningList)))));
/* mark column origins */
markTargetListOrigins(pstate, rlist);