Fix for #58422: Incorrect result when OUTER JOIN'ing with an empty table.

Fixed incorrect checks in join_read_const_table() for when to 
accept a non-existing, or empty const-row as a part of the const'ified 
set of tables.
      
Intention of this test is to only accept NULL-rows if this table is outer joined
into the resultset. (In case of an inner-join we can conclude at this point that 
resultset will be empty, end we want to return 'error' to signal this.)
      
Initially 'maybe_null' is set to the same value as 'outer_join' in 
setup_table_map(), mysql_priv.h ~line 2424. Later simplify_joins() will
attemp to replace outer joins by inner join whenever possible. This
will cause 'outer_join' to be updated. However, 'maybe_null' is *not* updated
to reflect this rewrite as this field is used to currectly set the 'nullability'
property for the columns in the resultset.
      
We should therefore change join_read_const_table() to check the 'outer_join'
property instead of 'maybe_null', as this correctly reflect the nullability of
the *execution plan* (not *resultset*).

1 files changed, 70 insertions, 0 deletions

diff --git a/mysql-test/t/select.test b/mysql-test/t/select.test
index 3ed7213e8d7..043b03e4686 100644
--- a/mysql-test/t/select.test
+++ b/mysql-test/t/select.test
@@ -4123,6 +4123,76 @@ SELECT 1 FROM t1 ORDER BY a COLLATE latin1_german2_ci;
 DROP TABLE t1;
 
 
+
+--echo #
+--echo # Bug #58422: Incorrect result when OUTER JOIN'ing 
+--echo # with an empty table
+--echo #
+
+CREATE TABLE t_empty(pk INT PRIMARY KEY, i INT) ENGINE = MYISAM;
+CREATE TABLE t1(pk INT PRIMARY KEY, i INT) ENGINE = MYISAM;
+INSERT INTO t1 VALUES (1,1), (2,2), (3,3);
+CREATE TABLE t2(pk INT PRIMARY KEY, i INT) ENGINE = MYISAM;
+INSERT INTO t2 VALUES (1,1), (2,2), (3,3);
+
+EXPLAIN
+SELECT *
+  FROM 
+    t1
+  LEFT OUTER JOIN
+    (t2 INNER JOIN t_empty ON TRUE)
+  ON t1.pk=t2.pk
+  WHERE t2.pk <> 2;
+
+SELECT *
+  FROM 
+    t1
+  LEFT OUTER JOIN
+    (t2 INNER JOIN t_empty ON TRUE)
+  ON t1.pk=t2.pk
+  WHERE t2.pk <> 2;
+
+
+EXPLAIN
+SELECT *
+  FROM 
+    t1
+  LEFT OUTER JOIN
+    (t2 CROSS JOIN t_empty)
+  ON t1.pk=t2.pk
+  WHERE t2.pk <> 2;
+
+SELECT *
+  FROM 
+    t1
+  LEFT OUTER JOIN
+    (t2 CROSS JOIN t_empty)
+  ON t1.pk=t2.pk
+  WHERE t2.pk <> 2;
+
+
+EXPLAIN
+SELECT *
+  FROM 
+    t1
+  LEFT OUTER JOIN
+    (t2 INNER JOIN t_empty ON t_empty.i=t2.i)
+  ON t1.pk=t2.pk
+  WHERE t2.pk <> 2;
+
+SELECT *
+  FROM 
+    t1
+  LEFT OUTER JOIN
+    (t2 INNER JOIN t_empty ON t_empty.i=t2.i)
+  ON t1.pk=t2.pk
+  WHERE t2.pk <> 2;
+
+
+
+DROP TABLE t1,t2,t_empty;
+
+
 --echo End of 5.1 tests
 
 --echo #