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.


sql/item_sum.h:
  Fixed bug#14169: type of group_concat() result changed to blob if tmp_table was 
  used
  The Item_func_group_concat::field_type() now returns FIELD_TYPE_BLOB if the result is longer than 512 chars.
tests/mysql_client_test.c:
  Added test case for bug#14169: type of group_concat() result changed to blob if tmp_table was used

sql/item_sum.h

@@ -1116,6 +1116,13 @@ 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_VARCHAR;
+  }
   void clear();
   bool add();
   void reset_field() { DBUG_ASSERT(0); }        // not used

tests/mysql_client_test.c

@@ -14841,6 +14841,40 @@ static void test_bug15613()
 }
 
 /*
+  Bug#14169: type of group_concat() result changed to blob if tmp_table was used
+*/
+static void test_bug14169()
+{
+  MYSQL_STMT *stmt;
+  const char *stmt_text;
+  MYSQL_RES *res;
+  MYSQL_FIELD *field;
+  int rc;
+
+  myheader("test_bug14169");
+
+  rc= mysql_query(mysql, "drop table if exists t1");
+  myquery(rc);
+  rc= mysql_query(mysql, "set session group_concat_max_len=1024");
+  myquery(rc);
+  rc= mysql_query(mysql, "create table t1 (f1 int unsigned, f2 varchar(255))");
+  myquery(rc);
+  rc= mysql_query(mysql, "insert into t1 values (1,repeat('a',255)),"
+                         "(2,repeat('b',255))");
+  myquery(rc);
+  stmt= mysql_stmt_init(mysql);
+  stmt_text= "select f2,group_concat(f1) from t1 group by f2";
+  rc= mysql_stmt_prepare(stmt, stmt_text, strlen(stmt_text));
+  myquery(rc);
+  res= mysql_stmt_result_metadata(stmt);
+  field= mysql_fetch_fields(res);
+  if (!opt_silent)
+    printf("GROUP_CONCAT() result type %i", field[1].type);
+  DIE_UNLESS(field[1].type == MYSQL_TYPE_BLOB);
+
+  rc= mysql_query(mysql, "drop table t1");
+  myquery(rc);
+}/*
   Read and parse arguments and MySQL options from my.cnf
 */
 
@@ -15105,6 +15139,7 @@ static struct my_tests_st my_tests[]= {
   { "test_bug16143", test_bug16143 },
   { "test_bug16144", test_bug16144 },
   { "test_bug15613", test_bug15613 },
+  { "test_bug14169", test_bug14169 },
   { 0, 0 }
 };