Fixed bug#14169: type of group_concat() result changed to blob if tmp_table was

used

In a simple queries a result of the GROUP_CONCAT() function was always of 
varchar type.
But if length of GROUP_CONCAT() result is greater than 512 chars and temporary
table is used during select then the result is converted to blob, due to
policy to not to store fields longer than 512 chars in tmp table as varchar
fields.

In order to provide consistent behaviour, result of GROUP_CONCAT() now
will always be converted to blob if it is longer than 512 chars.
Item_func_group_concat::field_type() is modified accordingly.

mysql-test/r/func_gconcat.result

@@ -604,3 +604,19 @@ count(distinct (f1+1))
 1
 3
 drop table t1;
+create table t1 (f1 int unsigned, f2 varchar(255));
+insert into t1 values (1,repeat('a',255)),(2,repeat('b',255));
+select f2,group_concat(f1) from t1 group by f2;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def	test	t1	t1	f2	f2	253	255	255	Y	0	0	8
+def					group_concat(f1)	252	400	1	Y	128	0	63
+f2	group_concat(f1)
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa	1
+bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb	2
+select f2,group_concat(f1) from t1 group by f2 order by 2;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def	test	t1	t1	f2	f2	253	255	255	Y	0	0	8
+def				group_concat(f1)	group_concat(f1)	252	400	1	Y	144	0	63
+f2	group_concat(f1)
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa	1
+bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb	2

mysql-test/t/func_gconcat.test

@@ -390,4 +390,14 @@ insert into t1 values(1),(2),(3);
 select f1, group_concat(f1+1) from t1 group by f1 with rollup;
 select count(distinct (f1+1)) from t1 group by f1 with rollup;
 drop table t1;
+
+#
+# Bug#14169 type of group_concat() result changed to blob if tmp_table was used
+#
+create table t1 (f1 int unsigned, f2 varchar(255));
+insert into t1 values (1,repeat('a',255)),(2,repeat('b',255));
+--enable_metadata
+select f2,group_concat(f1) from t1 group by f2;
+select f2,group_concat(f1) from t1 group by f2 order by 2;
+--disable_metadata
 # End of 4.1 tests

sql/item_func.cc

@@ -307,7 +307,7 @@ Field *Item_func::tmp_table_field(TABLE *t_arg)
     res= new Field_double(max_length, maybe_null, name, t_arg, decimals);
     break;
   case STRING_RESULT:
-    if (max_length > 255)
+    if (max_length/collation.collation->mbmaxlen > CONVERT_IF_BIGGER_TO_BLOB)
       res= new Field_blob(max_length, maybe_null, name, t_arg, collation.collation);
     else
       res= new Field_string(max_length, maybe_null, name, t_arg, collation.collation);

sql/item_sum.h

@@ -729,6 +729,13 @@ class Item_func_group_concat : public Item_sum
   enum Sumfunctype sum_func () const {return GROUP_CONCAT_FUNC;}
   const char *func_name() const { return "group_concat"; }
   virtual Item_result result_type () const { return STRING_RESULT; }
+  enum_field_types field_type() const
+  {
+    if (max_length/collation.collation->mbmaxlen > CONVERT_IF_BIGGER_TO_BLOB)
+      return FIELD_TYPE_BLOB;
+    else
+      return MYSQL_TYPE_VAR_STRING;
+  }
   void clear();
   bool add();
   void reset_field();

sql/sql_select.cc

@@ -4925,7 +4925,8 @@ static Field* create_tmp_field_from_item(THD *thd, Item *item, TABLE *table,
     if ((type= item->field_type()) == MYSQL_TYPE_DATETIME ||
         type == MYSQL_TYPE_TIME || type == MYSQL_TYPE_DATE)
       new_field= item->tmp_table_field_from_field_type(table);
-    else if (item->max_length/item->collation.collation->mbmaxlen > 255)
+    else if (item->max_length/item->collation.collation->mbmaxlen >
+             CONVERT_IF_BIGGER_TO_BLOB)
     {
       if (convert_blob_length)
         new_field= new Field_varstring(convert_blob_length, maybe_null,
@@ -5028,7 +5029,8 @@ Field *create_tmp_field(THD *thd, TABLE *table,Item *item, Item::Type type,
 	return new Field_longlong(item_sum->max_length,maybe_null,
 				  item->name,table,item->unsigned_flag);
       case STRING_RESULT:
-	if (item_sum->max_length > 255)
+	if (item_sum->max_length/item_sum->collation.collation->mbmaxlen >
+            CONVERT_IF_BIGGER_TO_BLOB)
         {
           if (convert_blob_length)
             return new Field_varstring(convert_blob_length, maybe_null,

sql/unireg.h

@@ -60,6 +60,7 @@
 
 #define MAX_MBWIDTH		3		/* Max multibyte sequence */
 #define MAX_FIELD_CHARLENGTH	255
+#define CONVERT_IF_BIGGER_TO_BLOB 255
 /* Max column width +1 */
 #define MAX_FIELD_WIDTH		(MAX_FIELD_CHARLENGTH*MAX_MBWIDTH+1)