diff --git a/mysql-test/r/func_group.result b/mysql-test/r/func_group.result
index e7f27ebb07e..1e130877088 100644
--- a/mysql-test/r/func_group.result
+++ b/mysql-test/r/func_group.result
@@ -1392,4 +1392,19 @@ SELECT MIN(b) FROM t1 WHERE a=1 AND b>'2007-08-01';
 MIN(b)
 NULL
 DROP TABLE t1;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3),(4);
+SET SQL_MODE=ONLY_FULL_GROUP_BY;
+SELECT a FROM t1 HAVING COUNT(*)>2;
+ERROR 42000: Mixing of GROUP columns (MIN(),MAX(),COUNT(),...) with no GROUP columns is illegal if there is no GROUP BY clause
+SELECT COUNT(*), a FROM t1;
+ERROR 42000: Mixing of GROUP columns (MIN(),MAX(),COUNT(),...) with no GROUP columns is illegal if there is no GROUP BY clause
+SET SQL_MODE=DEFAULT;
+SELECT a FROM t1 HAVING COUNT(*)>2;
+a
+1
+SELECT COUNT(*), a FROM t1;
+COUNT(*)	a
+4	1
+DROP TABLE t1;
 End of 5.0 tests
diff --git a/mysql-test/t/func_group.test b/mysql-test/t/func_group.test
index 7e115707625..25cb13a2f75 100644
--- a/mysql-test/t/func_group.test
+++ b/mysql-test/t/func_group.test
@@ -882,5 +882,24 @@ CREATE TABLE t1 (a int, b date NOT NULL, KEY k1 (a,b));
 SELECT MIN(b) FROM t1 WHERE a=1 AND b>'2007-08-01';
 DROP TABLE t1;
 
+#
+# Bug #31794: no syntax error on SELECT id FROM t HAVING count(*)>2;
+#
+
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3),(4);
+
+SET SQL_MODE=ONLY_FULL_GROUP_BY;
+--error ER_MIX_OF_GROUP_FUNC_AND_FIELDS
+SELECT a FROM t1 HAVING COUNT(*)>2;
+--error ER_MIX_OF_GROUP_FUNC_AND_FIELDS
+SELECT COUNT(*), a FROM t1;
+
+SET SQL_MODE=DEFAULT;
+SELECT a FROM t1 HAVING COUNT(*)>2;
+SELECT COUNT(*), a FROM t1;
+
+DROP TABLE t1;
+
 ###
 --echo End of 5.0 tests
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 7af39071561..e7d778de991 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -565,11 +565,12 @@ JOIN::prepare(Item ***rref_pointer_array,
   
 
   /*
-    Check if one one uses a not constant column with group functions
-    and no GROUP BY.
+    Check if there are references to un-aggregated columns when computing 
+    aggregate functions with implicit grouping (there is no GROUP BY).
     TODO:  Add check of calculation of GROUP functions and fields:
 	   SELECT COUNT(*)+table.col1 from table1;
   */
+  if (thd->variables.sql_mode & MODE_ONLY_FULL_GROUP_BY)
   {
     if (!group_list)
     {
@@ -583,6 +584,13 @@ JOIN::prepare(Item ***rref_pointer_array,
 	else if (!(flag & 2) && !item->const_during_execution())
 	  flag|=2;
       }
+      if (having)
+      {
+        if (having->with_sum_func)
+          flag |= 1;
+        else if (!having->const_during_execution())
+          flag |= 2;
+      }
       if (flag == 3)
       {
 	my_message(ER_MIX_OF_GROUP_FUNC_AND_FIELDS,