Fixed bug #51092.

The function JOIN_CACHE::read_all_record_fields could return 0
for an incremental join cache in two cases:
1. there were no more records in the associated join buffer
2. there was no table fields stored in the join buffer.
As a result the function JOIN_CACHE::get_record() could
return prematurely and did not read all needed fields from
join buffers into the record buffer.

Now the function JOIN_CACHE::read_all_record_fields returns
-1 if there are no more records in the associated join buffer.

1 files changed, 24 insertions, 0 deletions

diff --git a/mysql-test/t/join_cache.test b/mysql-test/t/join_cache.test
index 82fc37db641..0cb1c139161 100644
--- a/mysql-test/t/join_cache.test
+++ b/mysql-test/t/join_cache.test
@@ -1823,3 +1823,27 @@ SELECT t1.*, t2.*, LENGTH(t2.c1), LENGTH(t2.c2) FROM t1,t2
 set join_cache_level=default;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # Bug #51092: linked join buffer is used for a 3-way cross join query 
+--echo #             that selects only records of the first table
+--echo #
+
+create table t1 (a int, b int);
+insert into t1 values (1,1),(2,2);
+create table t2 (a int, b int);
+insert into t2 values (1,1),(2,2);
+create table t3 (a int, b int);
+insert into t3 values (1,1),(2,2);
+
+explain select t1.* from t1,t2,t3;
+select t1.* from t1,t2,t3; 
+
+set join_cache_level=2;
+
+explain select t1.* from t1,t2,t3;
+select t1.* from t1,t2,t3; 
+
+set join_cache_level=default;
+
+drop table t1,t2,t3;