fix(mysql): type untyped expression columns by value (SELECT 1 gone-away) - #8
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A prepared `SELECT 1` (or any table-less expression: `SELECT a+b`,
`SELECT 7 AS x`) dropped the connection with "2006 server has gone
away". SQLite gives expression columns no declared type, so decltype
is None and sqlite_to_mysql_column_type fell back to VAR_STRING — but
the row writer emits each value natively (an integer as LONGLONG), and
opensrv's binary protocol rejects the declared/actual mismatch
("tried to use 1 as MYSQL_TYPE_VAR_STRING") and closes the socket.
Fix: for columns with no decltype, derive the wire type from the first
non-NULL value in the result set (mysql_type_for_value), so the
declared column type matches how the value is encoded. Declared-type
columns are unchanged; all-NULL/empty columns stay VAR_STRING (NULL is
valid against any type).
Regression test prepared_select_expression_no_table covers SELECT 1,
a multi-column expression select, and an aliased expression. Found via
ePHPm DB probing; only bit clients that disable PDO prepare-emulation
(Doctrine-style) and issue a real-prepared expression query.
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Summary
SELECT 1(or any table-less expression:SELECT a+b,SELECT 7 AS x) dropped the connection with 2006 server has gone away.decltype = None→sqlite_to_mysql_column_typefell back toVAR_STRING. But the row writer emits each value natively (integer → LONGLONG), and opensrv's binary protocol rejects the declared/actual mismatch (tried to use 1 as MYSQL_TYPE_VAR_STRING) and closes the socket.decltype, derive the wire type from the first non-NULL value (mysql_type_for_value). Declared-type columns unchanged; all-NULL/empty columns stayVAR_STRING.Test
prepared_select_expression_no_table(SELECT 1, multi-column expression, aliased expression) — fails before, passes after.mysql_e2esuite: 24 passed. clippy-D warnings+ fmt clean.Found during ePHPm's DB verification. Impact: bit clients that disable PDO prepare-emulation (Doctrine-style) and issue a real-prepared expression query; direct
COM_QUERYwas unaffected. Not a v0.4.1 blocker (table queries work) but a clean correctness fix for the follow-up.