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-rw-r--r--mysql-test/r/subselect.result25
-rw-r--r--mysql-test/r/subselect4.result55
-rw-r--r--mysql-test/r/subselect_no_mat.result25
-rw-r--r--mysql-test/r/subselect_no_opts.result25
-rw-r--r--mysql-test/r/subselect_no_scache.result25
-rw-r--r--mysql-test/r/subselect_no_semijoin.result25
-rw-r--r--mysql-test/t/subselect.test18
-rw-r--r--mysql-test/t/subselect4.test34
-rw-r--r--sql/item_subselect.cc36
-rw-r--r--sql/item_subselect.h4
10 files changed, 270 insertions, 2 deletions
diff --git a/mysql-test/r/subselect.result b/mysql-test/r/subselect.result
index 235d211840f..936ffac6828 100644
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@@ -6589,5 +6589,30 @@ NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
SELECT SUM(a) AS f1, a AS f2 FROM (t1, t2) HAVING f2 >= ALL (SELECT 4 UNION SELECT 5) AND f1 = 7;
f1 f2
drop table t1,t2;
+#
+# LP BUG#1008686 Server crashes in subselect_union_engine::no_rows on SELECT with impossible
+# WHERE and UNION in HAVING
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(7);
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used
+3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+min_a a
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where
+3 DEPENDENT UNION t1 ALL NULL NULL NULL NULL 2 Using where
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+min_a a
+drop table t1;
# return optimizer switch changed in the beginning of this test
set optimizer_switch=@subselect_tmp;
diff --git a/mysql-test/r/subselect4.result b/mysql-test/r/subselect4.result
index 617d2e9e592..cb515b3c3d5 100644
--- a/mysql-test/r/subselect4.result
+++ b/mysql-test/r/subselect4.result
@@ -2029,6 +2029,61 @@ id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 10 Using where
2 SUBQUERY five ALL NULL NULL NULL NULL 5 Using where
drop table ten, t1, five;
+#
+# LP BUG#1008773 Wrong result (NULL instead of a value) with no matching rows, subquery in FROM and HAVING
+#
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+CREATE TABLE t2 (b INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1);
+EXPLAIN
+SELECT MAX(a), ( SELECT 1 FROM t2 ) AS bb FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found
+2 SUBQUERY t2 system NULL NULL NULL NULL 1
+SELECT MAX(a), ( SELECT 1 FROM t2 ) AS bb FROM t1;
+MAX(a) bb
+NULL 1
+EXPLAIN
+SELECT MAX(a), 1 in ( SELECT b FROM t2 ) AS bb FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found
+2 SUBQUERY t2 system NULL NULL NULL NULL 1
+SELECT MAX(a), 1 in ( SELECT b FROM t2 ) AS bb FROM t1;
+MAX(a) bb
+NULL 1
+EXPLAIN
+SELECT MAX(a), 1 >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found
+2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
+SELECT MAX(a), 1 >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+MAX(a) bb
+NULL 1
+EXPLAIN
+SELECT MAX(a), ( SELECT 1 FROM t2 where b = a) AS bb FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found
+2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
+SELECT MAX(a), ( SELECT 1 FROM t2 where b = a) AS bb FROM t1;
+MAX(a) bb
+NULL NULL
+EXPLAIN
+SELECT MAX(a), a in ( SELECT b FROM t2 ) AS bb FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found
+2 DEPENDENT SUBQUERY t2 system NULL NULL NULL NULL 1
+SELECT MAX(a), a in ( SELECT b FROM t2 ) AS bb FROM t1;
+MAX(a) bb
+NULL NULL
+EXPLAIN
+SELECT MAX(a), a >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found
+2 DEPENDENT SUBQUERY t2 system NULL NULL NULL NULL 1
+SELECT MAX(a), a >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+MAX(a) bb
+NULL NULL
+drop table t1, t2;
set optimizer_switch=@subselect4_tmp;
SET optimizer_switch= @@global.optimizer_switch;
set @@tmp_table_size= @@global.tmp_table_size;
diff --git a/mysql-test/r/subselect_no_mat.result b/mysql-test/r/subselect_no_mat.result
index b08148f8057..3ef60cdef85 100644
--- a/mysql-test/r/subselect_no_mat.result
+++ b/mysql-test/r/subselect_no_mat.result
@@ -6588,6 +6588,31 @@ NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
SELECT SUM(a) AS f1, a AS f2 FROM (t1, t2) HAVING f2 >= ALL (SELECT 4 UNION SELECT 5) AND f1 = 7;
f1 f2
drop table t1,t2;
+#
+# LP BUG#1008686 Server crashes in subselect_union_engine::no_rows on SELECT with impossible
+# WHERE and UNION in HAVING
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(7);
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used
+3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+min_a a
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where
+3 DEPENDENT UNION t1 ALL NULL NULL NULL NULL 2 Using where
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+min_a a
+drop table t1;
# return optimizer switch changed in the beginning of this test
set optimizer_switch=@subselect_tmp;
set optimizer_switch=default;
diff --git a/mysql-test/r/subselect_no_opts.result b/mysql-test/r/subselect_no_opts.result
index 36d03d8db77..7d0aa2d8260 100644
--- a/mysql-test/r/subselect_no_opts.result
+++ b/mysql-test/r/subselect_no_opts.result
@@ -6584,6 +6584,31 @@ NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
SELECT SUM(a) AS f1, a AS f2 FROM (t1, t2) HAVING f2 >= ALL (SELECT 4 UNION SELECT 5) AND f1 = 7;
f1 f2
drop table t1,t2;
+#
+# LP BUG#1008686 Server crashes in subselect_union_engine::no_rows on SELECT with impossible
+# WHERE and UNION in HAVING
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(7);
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used
+3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+min_a a
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where
+3 DEPENDENT UNION t1 ALL NULL NULL NULL NULL 2 Using where
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+min_a a
+drop table t1;
# return optimizer switch changed in the beginning of this test
set optimizer_switch=@subselect_tmp;
set @optimizer_switch_for_subselect_test=null;
diff --git a/mysql-test/r/subselect_no_scache.result b/mysql-test/r/subselect_no_scache.result
index 7fcacfda470..4c770063468 100644
--- a/mysql-test/r/subselect_no_scache.result
+++ b/mysql-test/r/subselect_no_scache.result
@@ -6595,6 +6595,31 @@ NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
SELECT SUM(a) AS f1, a AS f2 FROM (t1, t2) HAVING f2 >= ALL (SELECT 4 UNION SELECT 5) AND f1 = 7;
f1 f2
drop table t1,t2;
+#
+# LP BUG#1008686 Server crashes in subselect_union_engine::no_rows on SELECT with impossible
+# WHERE and UNION in HAVING
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(7);
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used
+3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+min_a a
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where
+3 DEPENDENT UNION t1 ALL NULL NULL NULL NULL 2 Using where
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+min_a a
+drop table t1;
# return optimizer switch changed in the beginning of this test
set optimizer_switch=@subselect_tmp;
set optimizer_switch=default;
diff --git a/mysql-test/r/subselect_no_semijoin.result b/mysql-test/r/subselect_no_semijoin.result
index 405261c9ec6..6927abb21fd 100644
--- a/mysql-test/r/subselect_no_semijoin.result
+++ b/mysql-test/r/subselect_no_semijoin.result
@@ -6584,6 +6584,31 @@ NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
SELECT SUM(a) AS f1, a AS f2 FROM (t1, t2) HAVING f2 >= ALL (SELECT 4 UNION SELECT 5) AND f1 = 7;
f1 f2
drop table t1,t2;
+#
+# LP BUG#1008686 Server crashes in subselect_union_engine::no_rows on SELECT with impossible
+# WHERE and UNION in HAVING
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(7);
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used
+3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+min_a a
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
+2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where
+3 DEPENDENT UNION t1 ALL NULL NULL NULL NULL 2 Using where
+NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+min_a a
+drop table t1;
# return optimizer switch changed in the beginning of this test
set optimizer_switch=@subselect_tmp;
set @optimizer_switch_for_subselect_test=null;
diff --git a/mysql-test/t/subselect.test b/mysql-test/t/subselect.test
index b02b1d4a4a0..0fb3ae9bb6a 100644
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@@ -5556,5 +5556,23 @@ SELECT SUM(a) AS f1, a AS f2 FROM (t1, t2) HAVING f2 >= ALL (SELECT 4 UNION SELE
drop table t1,t2;
+--echo #
+--echo # LP BUG#1008686 Server crashes in subselect_union_engine::no_rows on SELECT with impossible
+--echo # WHERE and UNION in HAVING
+--echo #
+
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(7);
+
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 0 HAVING a NOT IN ( SELECT 2 UNION SELECT 5 ) OR min_a != 1;
+
+EXPLAIN
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+SELECT MIN(a) AS min_a, a FROM t1 WHERE 1=2 HAVING a NOT IN ( SELECT a from t1 UNION select a+1 from t1 ) OR min_a != 1;
+
+drop table t1;
+
--echo # return optimizer switch changed in the beginning of this test
set optimizer_switch=@subselect_tmp;
diff --git a/mysql-test/t/subselect4.test b/mysql-test/t/subselect4.test
index e6ff625d3fe..832d6d85c21 100644
--- a/mysql-test/t/subselect4.test
+++ b/mysql-test/t/subselect4.test
@@ -1663,6 +1663,40 @@ explain select * from t1 where 33 in (select b from five) or c > 11;
drop table ten, t1, five;
+--echo #
+--echo # LP BUG#1008773 Wrong result (NULL instead of a value) with no matching rows, subquery in FROM and HAVING
+--echo #
+
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+CREATE TABLE t2 (b INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1);
+
+EXPLAIN
+SELECT MAX(a), ( SELECT 1 FROM t2 ) AS bb FROM t1;
+SELECT MAX(a), ( SELECT 1 FROM t2 ) AS bb FROM t1;
+
+EXPLAIN
+SELECT MAX(a), 1 in ( SELECT b FROM t2 ) AS bb FROM t1;
+SELECT MAX(a), 1 in ( SELECT b FROM t2 ) AS bb FROM t1;
+
+EXPLAIN
+SELECT MAX(a), 1 >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+SELECT MAX(a), 1 >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+
+
+EXPLAIN
+SELECT MAX(a), ( SELECT 1 FROM t2 where b = a) AS bb FROM t1;
+SELECT MAX(a), ( SELECT 1 FROM t2 where b = a) AS bb FROM t1;
+
+EXPLAIN
+SELECT MAX(a), a in ( SELECT b FROM t2 ) AS bb FROM t1;
+SELECT MAX(a), a in ( SELECT b FROM t2 ) AS bb FROM t1;
+
+EXPLAIN
+SELECT MAX(a), a >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+SELECT MAX(a), a >= ALL ( SELECT b FROM t2 ) AS bb FROM t1;
+
+drop table t1, t2;
set optimizer_switch=@subselect4_tmp;
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 4acac68fe6b..9a3f5bd8a51 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -904,6 +904,15 @@ void Item_maxmin_subselect::print(String *str, enum_query_type query_type)
void Item_maxmin_subselect::no_rows_in_result()
{
+ /*
+ Subquery predicates outside of the SELECT list must be evaluated in order
+ to possibly filter the special result row generated for implicit grouping
+ if the subquery is in the HAVING clause.
+ If the predicate is constant, we need its actual value in the only result
+ row for queries with implicit grouping.
+ */
+ if (parsing_place != SELECT_LIST || const_item())
+ return;
value= Item_cache::get_cache(new Item_null());
null_value= 0;
was_values= 0;
@@ -913,6 +922,15 @@ void Item_maxmin_subselect::no_rows_in_result()
void Item_singlerow_subselect::no_rows_in_result()
{
+ /*
+ Subquery predicates outside of the SELECT list must be evaluated in order
+ to possibly filter the special result row generated for implicit grouping
+ if the subquery is in the HAVING clause.
+ If the predicate is constant, we need its actual value in the only result
+ row for queries with implicit grouping.
+ */
+ if (parsing_place != SELECT_LIST || const_item())
+ return;
value= Item_cache::get_cache(new Item_null());
reset();
make_const();
@@ -1375,6 +1393,15 @@ Item* Item_exists_subselect::expr_cache_insert_transformer(uchar *thd_arg)
void Item_exists_subselect::no_rows_in_result()
{
+ /*
+ Subquery predicates outside of the SELECT list must be evaluated in order
+ to possibly filter the special result row generated for implicit grouping
+ if the subquery is in the HAVING clause.
+ If the predicate is constant, we need its actual value in the only result
+ row for queries with implicit grouping.
+ */
+ if (parsing_place != SELECT_LIST || const_item())
+ return;
value= 0;
null_value= 0;
make_const();
@@ -2719,6 +2746,15 @@ void Item_allany_subselect::print(String *str, enum_query_type query_type)
void Item_allany_subselect::no_rows_in_result()
{
+ /*
+ Subquery predicates outside of the SELECT list must be evaluated in order
+ to possibly filter the special result row generated for implicit grouping
+ if the subquery is in the HAVING clause.
+ If the predicate is constant, we need its actual value in the only result
+ row for queries with implicit grouping.
+ */
+ if (parsing_place != SELECT_LIST || const_item())
+ return;
value= 0;
null_value= 0;
was_null= 0;
diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 0e0f61aedd9..6b00cd18d6e 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -159,8 +159,8 @@ public:
null_value= 1;
}
/**
- Set the subquery result to the default value for the predicate when the
- subquery is known to produce an empty result.
+ Set the subquery result to a default value consistent with the semantics of
+ the result row produced for queries with implicit grouping.
*/
void no_rows_in_result()= 0;
virtual bool select_transformer(JOIN *join);