Fix for lp:780425 sql_buffer_result=1 gives wrong result for GROUP BY with a...

Fix for lp:780425 sql_buffer_result=1 gives wrong result for GROUP BY with a +# constant expression"

mysql-test/r/select.result:
  Test case for lp:780425
mysql-test/r/select_pkeycache.result:
  lp:780425
mysql-test/t/select.test:
  lp:780425
sql/sql_select.cc:
  Added DBUG_ASSERT to be prove some logic and later be able to simplify the code
  Set implicit_grouping if we delete a GROUP BY to signal do_select() that a grouping needs to be done.

mysql-test/r/select.result

@@ -4875,4 +4875,31 @@ f1	f1	f1	f1	f2	f1	f1
 18	9	NULL	NULL	NULL	5	7
 SET SESSION join_buffer_size = DEFAULT;
 DROP TABLE t1,t2,t3,t4,t5,t6;
+CREATE TABLE t1(f1 int UNSIGNED) engine=myisam;
+INSERT INTO t1 VALUES (3),(2),(1);
+set sql_buffer_result=0;
+SELECT f1 FROM t1 GROUP BY 1;
+f1
+1
+2
+3
+SELECT f1 FROM t1 GROUP BY '123' = 'abc';
+f1
+3
+SELECT 1 FROM t1 GROUP BY 1;
+1
+1
+set sql_buffer_result=1;
+SELECT f1 FROM t1 GROUP BY 1;
+f1
+1
+2
+3
+SELECT f1 FROM t1 GROUP BY '123' = 'abc';
+f1
+3
+SELECT 1 FROM t1 GROUP BY 1;
+1
+1
+drop table t1;
 End of 5.1 tests

mysql-test/r/select_pkeycache.result

@@ -4875,4 +4875,31 @@ f1	f1	f1	f1	f2	f1	f1
 18	9	NULL	NULL	NULL	5	7
 SET SESSION join_buffer_size = DEFAULT;
 DROP TABLE t1,t2,t3,t4,t5,t6;
+CREATE TABLE t1(f1 int UNSIGNED) engine=myisam;
+INSERT INTO t1 VALUES (3),(2),(1);
+set sql_buffer_result=0;
+SELECT f1 FROM t1 GROUP BY 1;
+f1
+1
+2
+3
+SELECT f1 FROM t1 GROUP BY '123' = 'abc';
+f1
+3
+SELECT 1 FROM t1 GROUP BY 1;
+1
+1
+set sql_buffer_result=1;
+SELECT f1 FROM t1 GROUP BY 1;
+f1
+1
+2
+3
+SELECT f1 FROM t1 GROUP BY '123' = 'abc';
+f1
+3
+SELECT 1 FROM t1 GROUP BY 1;
+1
+1
+drop table t1;
 End of 5.1 tests

mysql-test/t/select.test

@@ -4121,4 +4121,21 @@ SET SESSION join_buffer_size = DEFAULT;
 
 DROP TABLE t1,t2,t3,t4,t5,t6;
 
+#
+# Bug #780425: "sql_buffer_result=1 gives wrong result for GROUP BY with a
+# constant expression"
+#
+
+CREATE TABLE t1(f1 int UNSIGNED) engine=myisam;
+INSERT INTO t1 VALUES (3),(2),(1);
+set sql_buffer_result=0;
+SELECT f1 FROM t1 GROUP BY 1;
+SELECT f1 FROM t1 GROUP BY '123' = 'abc';
+SELECT 1 FROM t1 GROUP BY 1;
+set sql_buffer_result=1;
+SELECT f1 FROM t1 GROUP BY 1;
+SELECT f1 FROM t1 GROUP BY '123' = 'abc';
+SELECT 1 FROM t1 GROUP BY 1;
+drop table t1;
+
 --echo End of 5.1 tests

sql/sql_select.cc

@@ -1295,14 +1295,18 @@ JOIN::optimize()
       DBUG_RETURN(1);
     }
     if (old_group_list && !group_list)
+    {
+      DBUG_ASSERT(group);
       select_distinct= 0;
     }
+  }
   if (!group_list && group)
   {
     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;
+    implicit_grouping= TRUE;
   }
 
   calc_group_buffer(this, group_list);