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MDEV-31279 Crash when lateral derived is guaranteed to return no rows

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Consider this query
SELECT t1.* FROM t1, (SELECT t2.b FROM t2 WHERE NOT EXISTS
(SELECT 1 FROM t3) GROUP BY b) sq where sq.b = t1.a;

If SELECT 1 FROM t3 is expensive, for example t3 has >
thd->variables.expensive_subquery_limit, first evaluation is deferred to
mysql_derived_fill().  There it is noted that, in the above case
 NOT EXISTS (SELECT 1 FROM t3) is constant and false.

This causes the join variable zero_result_cause to be set to
"Impossible WHERE noticed after reading const tables" and the handler
for this join is never "opened" via handler::ha_open.

When mysql_derived_fill() is called for the next group of results, this
unopened handler is not taken into account.

reviewed by Igor Babaev (igor@mariadb.com)
This commit is contained in:
Rex
2023-10-11 15:05:58 +12:00
committed by Rex Johnston
parent c17aca2f11
commit b4712242dd
3 changed files with 36 additions and 0 deletions
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3
sql/sql_derived.cc
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@ -1227,6 +1227,9 @@ bool mysql_derived_fill(THD *thd, LEX *lex, TABLE_LIST *derived)
goto err;
JOIN *join= unit->first_select()->join;
join->first_record= false;
if (join->zero_result_cause)
goto err;
for (uint i= join->top_join_tab_count;
i < join->top_join_tab_count + join->aggr_tables;
i++)