Bug #29717 INSERT INTO SELECT inserts values even if

 SELECT statement itself returns empty.

As a result of this bug 'SELECT AGGREGATE_FUNCTION(fld) ... GROUP BY'
can return one row instead of an empty result set.

When GROUP BY only has fields of constant tables
(with a single row), the optimizer deletes the group_list.
After that we lose the information about whether we had an
GROUP BY statement. Though it's important
as SELECT min(x) from empty_table; and
   SELECT min(x) from empty_table GROUP BY y; have to return
different results - the first query should return one row,
second - an empty result set.
So here we add the 'group_optimized_away' flag to remember this case
when GROUP BY exists in the query and is removed
by the optimizer, and check this flag in end_send_group()

mysql-test/r/group_by.result

@@ -818,3 +818,20 @@ a
 2
 1
 DROP TABLE t1;
+CREATE TABLE t1 (
+f1 int(10) unsigned NOT NULL auto_increment primary key,
+f2 varchar(100) NOT NULL default ''
+);
+CREATE TABLE t2 (
+f1 varchar(10) NOT NULL default '',
+f2 char(3) NOT NULL default '',
+PRIMARY KEY  (`f1`),
+KEY `k1` (`f2`,`f1`)
+);
+INSERT INTO t1 values(NULL, '');
+INSERT INTO `t2` VALUES ('486878','WDT'),('486910','WDT');
+SELECT SQL_BUFFER_RESULT avg(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+avg(t2.f1)
+SELECT avg(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+avg(t2.f1)
+DROP TABLE t1, t2;

mysql-test/r/insert_select.result

@@ -690,3 +690,29 @@ CREATE TABLE t1 (a int PRIMARY KEY);
 INSERT INTO t1 values (1), (2);
 INSERT INTO t1 SELECT a + 2 FROM t1 LIMIT 1;
 DROP TABLE t1;
+CREATE TABLE t1 (
+f1 int(10) unsigned NOT NULL auto_increment PRIMARY KEY,
+f2 varchar(100) NOT NULL default ''
+);
+CREATE TABLE t2 (
+f1 varchar(10) NOT NULL default '',
+f2 char(3) NOT NULL default '',
+PRIMARY KEY  (`f1`),
+KEY `k1` (`f2`, `f1`)
+);
+INSERT INTO t1 values(NULL, '');
+INSERT INTO `t2` VALUES ('486878','WDT'),('486910','WDT');
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+1
+SELECT min(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+min(t2.f1)
+INSERT INTO t1 (f2)
+SELECT min(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+1
+SELECT * FROM t1;
+f1	f2
+1	
+DROP TABLE t1, t2;

mysql-test/t/group_by.test

@@ -633,4 +633,27 @@ SELECT a FROM t1 ORDER BY 'a' DESC;
 SELECT a FROM t1 ORDER BY "a" DESC;
 SELECT a FROM t1 ORDER BY `a` DESC;
 DROP TABLE t1;
+
+
+#
+# Bug #29717 INSERT INTO SELECT inserts values even if SELECT statement itself
+# returns empty
+# 
+CREATE TABLE t1 (
+    f1 int(10) unsigned NOT NULL auto_increment primary key,
+    f2 varchar(100) NOT NULL default ''
+);
+CREATE TABLE t2 (
+    f1 varchar(10) NOT NULL default '',
+    f2 char(3) NOT NULL default '',
+    PRIMARY KEY  (`f1`),
+    KEY `k1` (`f2`,`f1`)
+);
+
+INSERT INTO t1 values(NULL, '');
+INSERT INTO `t2` VALUES ('486878','WDT'),('486910','WDT');
+SELECT SQL_BUFFER_RESULT avg(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+SELECT avg(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+DROP TABLE t1, t2;
+
 # End of 4.1 tests

mysql-test/t/insert_select.test

@@ -239,4 +239,32 @@ INSERT INTO t1 SELECT a + 2 FROM t1 LIMIT 1;
 
 DROP TABLE t1;
 
+#
+# Bug #29717 INSERT INTO SELECT inserts values even if SELECT statement itself returns empty
+#
+
+CREATE TABLE t1 (
+    f1 int(10) unsigned NOT NULL auto_increment PRIMARY KEY,
+    f2 varchar(100) NOT NULL default ''
+);
+CREATE TABLE t2 (
+    f1 varchar(10) NOT NULL default '',
+    f2 char(3) NOT NULL default '',
+    PRIMARY KEY  (`f1`),
+    KEY `k1` (`f2`, `f1`)
+);
+
+INSERT INTO t1 values(NULL, '');
+INSERT INTO `t2` VALUES ('486878','WDT'),('486910','WDT');
+SELECT COUNT(*) FROM t1;
+
+SELECT min(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+
+INSERT INTO t1 (f2)
+  SELECT min(t2.f1) FROM t1, t2 where t2.f2 = 'SIR' GROUP BY t1.f1;
+
+SELECT COUNT(*) FROM t1;
+SELECT * FROM t1;
+DROP TABLE t1, t2;
+
 # End of 4.1 tests

sql/sql_select.cc

@@ -777,6 +777,7 @@ JOIN::optimize()
     order=0;					// The output has only one row
     simple_order=1;
     select_distinct= 0;                       // No need in distinct for 1 row
+    group_optimized_away= 1;
   }
 
   calc_group_buffer(this, group_list);
@@ -6896,7 +6897,8 @@ end_send_group(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
   if (!join->first_record || end_of_records ||
       (idx=test_if_group_changed(join->group_fields)) >= 0)
   {
-    if (join->first_record || (end_of_records && !join->group))
+    if (join->first_record || 
+        (end_of_records && !join->group && !join->group_optimized_away))
     {
       if (join->procedure)
 	join->procedure->end_group();

sql/sql_select.h

@@ -180,6 +180,14 @@ class JOIN :public Sql_alloc
   ROLLUP rollup;				// Used with rollup
 
   bool select_distinct;				// Set if SELECT DISTINCT
+  /*
+    If we have the GROUP BY statement in the query,
+    but the group_list was emptied by optimizer, this
+    flag is TRUE.
+    It happens when fields in the GROUP BY are from
+    constant table
+  */
+  bool group_optimized_away;
 
   /*
     simple_xxxxx is set if ORDER/GROUP BY doesn't include any references
@@ -276,6 +284,7 @@ class JOIN :public Sql_alloc
     ref_pointer_array_size= 0;
     zero_result_cause= 0;
     optimized= 0;
+    group_optimized_away= 0;
 
     fields_list= fields_arg;
     bzero((char*) &keyuse,sizeof(keyuse));