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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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15
src/test/regress/sql/errors.sql
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@ -16,28 +16,25 @@ select 1;
--
-- SELECT
-- missing relation name
-- this used to be a syntax error, but now we allow an empty target list
select;
-- no such relation
select * from nonesuch;
-- missing target list
select from pg_database;
-- bad name in target list
select nonesuch from pg_database;
-- empty distinct list isn't OK
select distinct from pg_database;
-- bad attribute name on lhs of operator
select * from pg_database where nonesuch = pg_database.datname;
-- bad attribute name on rhs of operator
select * from pg_database where pg_database.datname = nonesuch;
-- bad select distinct on syntax, distinct attribute missing
select distinct on (foobar) from pg_database;
-- bad select distinct on syntax, distinct attribute not in target list
-- bad attribute name in select distinct on
select distinct on (foobar) * from pg_database;