Bug#51494 crash with join, explain and 'sounds like' operator

The crash happens because of discrepancy between values of
conts_tables and join->const_table_map(make_join_statisctics).
Calculation of conts_tables used condition with
HA_STATS_RECORDS_IS_EXACT flag check. Calculation of
join->const_table_map does not use this flag check.
In case of MERGE table without union with index
the table does not become const table and
thus join_read_const_table() is not called
for the table. join->const_table_map supposes
this table is const and later in make_join_select
this table is used for making&calculation const
condition. As table record buffer is not populated
it leads to crash.
The fix is adding a check if an engine supports
HA_STATS_RECORDS_IS_EXACT flag before updating
join->const_table_map.


mysql-test/r/merge.result:
  test result
mysql-test/t/merge.test:
  test case
sql/sql_select.cc:
  adding a check if an engine supports
  HA_STATS_RECORDS_IS_EXACT flag before updating
  join->const_table_map.

1 files changed, 15 insertions, 0 deletions

diff --git a/mysql-test/t/merge.test b/mysql-test/t/merge.test
index d88467cc7a9..44b202fab97 100644
--- a/mysql-test/t/merge.test
+++ b/mysql-test/t/merge.test
@@ -1690,4 +1690,19 @@ DROP TABLE m1;
 DROP TABLE `test@1`.`t@1`;
 DROP DATABASE `test@1`;
 
+--echo #
+--echo # Bug#51494c rash with join, explain and 'sounds like' operator
+--echo #
+
+CREATE TABLE t1 (a INT) ENGINE=MYISAM;
+INSERT INTO t1 VALUES(1);
+
+CREATE TABLE t2 (b INT NOT NULL,c INT,d INT,e BLOB NOT NULL,
+KEY idx0 (d, c)) ENGINE=MERGE;
+
+EXPLAIN SELECT * FROM t1 NATURAL RIGHT JOIN
+t2 WHERE b SOUNDS LIKE e AND d = 1;
+
+DROP TABLE t2, t1;
+
 --echo End of 5.1 tests