From 90780bb5a949d5e27b39df4adaa1d7b1ad98948e Mon Sep 17 00:00:00 2001 From: Igor Babaev Date: Wed, 10 Mar 2021 17:26:43 -0800 Subject: MDEV-21104 Wrong result (extra rows and wrong values) with incremental BNLH This bug could affect multi-way join queries with embedded outer joins that contained a conjunctive IS NULL predicate over a non-nullable column from inner table of an outer join. The predicate could occur in WHERE condition or in ON condition. Due to this bug a wrong result set could be returned by the query. The bug manifested itself only when join buffers were employed for join operations. The problem appeared because - a bug in the function JOIN_CACHE::get_match_flag_by_pos that not always returned proper match flags for embedding outer joins stored together with table rows put a join buffer. - bug in the function JOIN_CACHE::join_matching_records that not always correctly determined that a row from the buffer could be skipped due to applied 'not_exists' optimization. Example: SELECT * FROM t1 LEFT JOIN ((t2 LEFT JOIN t3 ON c = d) JOIN t4) ON b = e WHERE e IS NULL; The patch introduces a new function that finds the match flag for a record from join buffer specifying the buffer where this flag has to be found. The function is called JOIN_CACHE::get_match_flag_by_pos_from_join_buffer(). Now this function rather than JOIN_CACHE::get_match_flag_by_pos() is used in JOIN_CACHE::skip_if_matched() to check whether a record from the join buffer must be ignored when extending the record by null complements. Also the code of the function JOIN_CACHE::skip_if_not_needed_match() has been changed. The function checks whether a record from the join buffer still may produce some useful extensions. Also some clarifying comments has been added. Approved by monty@mariadb.com. --- sql/sql_join_cache.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'sql/sql_join_cache.h') diff --git a/sql/sql_join_cache.h b/sql/sql_join_cache.h index 1cbc6acfd79..456991037d1 100644 --- a/sql/sql_join_cache.h +++ b/sql/sql_join_cache.h @@ -206,7 +206,9 @@ protected: /* This flag indicates that records written into the join buffer contain - a match flag field. The flag must be set by the init method. + a match flag field. The flag must be set by the init method. + Currently any implementation of the virtial init method calls + the function JOIN_CACHE::calc_record_fields() to set this flag. */ bool with_match_flag; /* @@ -646,6 +648,13 @@ public: /* Shall return the value of the match flag for the positioned record */ virtual enum Match_flag get_match_flag_by_pos(uchar *rec_ptr); + /* + Shall return the value of the match flag for the positioned record + from the join buffer attached to the specified table + */ + virtual enum Match_flag + get_match_flag_by_pos_from_join_buffer(uchar *rec_ptr, JOIN_TAB *tab); + /* Shall return the position of the current record */ virtual uchar *get_curr_rec() { return curr_rec_pos; } -- cgit v1.2.1