The driver chose between "open a cursor and fetch" and "execute and
release" by checking whether the first word of the SQL was SELECT. That
misses a leading comment in any of the three Informix flavours (--,
/* */, { }), a parenthesized select, a parenthesized UNION, and a CTE.
All five are perfectly ordinary queries. All five failed with -260,
"Cursor name already in use" -- an error that describes neither the
cause nor anything the caller did. It says "cursor" because the driver
sent SQ_EXECUTE where the server was waiting to open one.
The server had been answering this question all along. statement_type is
the first field of the DESCRIBE response and parse_describe has always
put it in the metadata dict, where nothing read it.
The comment defending the heuristic said nfields couldn't distinguish
these cases because INSERT INTO t VALUES (?) also describes a column.
That was true, and it argued for the wrong conclusion: statement_type
distinguishes them exactly. Measured against all three servers -- every
SELECT form above reports 2, that INSERT reports 6, UPDATE 33, DELETE
32, CREATE 45, EXECUTE PROCEDURE 56.
The predicate is now JDBC's IfxSqli.isResultSet: type 2, or type 56 with
at least one column, since a routine may or may not return rows. That
last clause fixes EXECUTE FUNCTION as a side effect -- it used to run
down the DML path and discard the return value. It now yields it.
executemany keeps the first-word check as a cheap pre-flight reject, and
gains an authoritative one after PREPARE for the forms the first word
misses. The refusal releases the statement, so the connection survives.
Informix 12.10 has no CTEs and rejects WITH with -201 at offset 1. That
is the server declining the grammar rather than the driver routing it
wrongly, and the test skips on it.
