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Looking at union.result in 10.1 code, one can see:
# # Bug #49734: Crash on EXPLAIN EXTENDED UNION ... ORDER BY # <any non-const-function> # CREATE TABLE t1 (a VARCHAR(10), FULLTEXT KEY a (a)); INSERT INTO t1 VALUES (1),(2); CREATE TABLE t2 (b INT); INSERT INTO t2 VALUES (1),(2);
...
EXPLAIN EXTENDED SELECT * FROM t1 UNION SELECT * FROM t1 ORDER BY (SELECT a FROM t2 WHERE b = 12); id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY t1 ALL NULL NULL NULL NULL 2 100.00 2 UNION t1 ALL NULL NULL NULL NULL 2 100.00 NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL NULL Using filesort 3 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 100.00 Using where Warnings: Note 1276 Field or reference 'a' of SELECT #3 was resolved in SELECT #-1 Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` union select `test`.`t1`.`a` AS `a` from `test`.`t1` order by <expr_cache><>((select `a` from `test`.`t2` where (`test`.`t2`.`b` = 12)))
Note this:
<expr_cache><>((select `a` from `test`.`t2` where (`test`.`t2`.`b` = 12)))
The subquery is actually dependent, and it is incorrect that we see "<expr_cache><>" and not "<expr_cache><a>".
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Investigated together with Oleksandr Byelkin.
The subquery cache didn't register dependency on 'a', because of the following:
<spetrunia> bool Item_ident::collect_outer_ref_processor(uchar *param) <spetrunia> { <spetrunia> Collect_deps_prm *prm= (Collect_deps_prm *)param; <spetrunia> if (depended_from && <spetrunia> depended_from->nest_level_base == prm->nest_level_base && <spetrunia> depended_from->nest_level < prm->nest_level) <spetrunia> (gdb) print depended_from <spetrunia> $28 = (st_select_lex *) 0x7fff940720a0 <spetrunia> (gdb) p depended_from->nest_level_base <spetrunia> $29 = (SELECT_LEX_UNIT *) 0x4 <spetrunia> (gdb) p prm->nest_level_base <spetrunia> $30 = (st_select_lex_unit *) 0x2cff6c0 <spetrunia> (gdb) p/x depended_from->select_number <spetrunia> $33 = 0xfffffffffake_select_lex objects have invalid data in nest_level and nest_level_base. These members are never set.