BUG#21635: MYSQL_FIELD struct's member strings seem to misbehave for

expression cols.

The problem was that MYSQL_FIELD::org_name was set for MIN() and MAX()
functions (COUNT() is also mentioned in the bug report but was already
fixed).

After this patch for expressions MYSQL_FIELD::name is set to either
expression itself or its alias, and other data origin fields of
MYSQL_FILED (db, org_table, table, org_name) are empty strings.


sql/item_sum.cc:
  For expressions only col_name should be non-empty string.
tests/mysql_client_test.c:
  Add test case for bug#21635: MYSQL_FIELD struct's member strings seem
  to misbehave for expression cols.

sql/item_sum.cc

@@ -71,9 +71,13 @@ void Item_sum::make_field(Send_field *tmp_field)
   if (args[0]->type() == Item::FIELD_ITEM && keep_field_type())
   {
     ((Item_field*) args[0])->field->make_field(tmp_field);
-    tmp_field->db_name=(char*)"";
-    tmp_field->org_table_name=tmp_field->table_name=(char*)"";
-    tmp_field->org_col_name=tmp_field->col_name=name;
+    /* For expressions only col_name should be non-empty string. */
+    char *empty_string= (char*)"";
+    tmp_field->db_name= empty_string;
+    tmp_field->org_table_name= empty_string;
+    tmp_field->table_name= empty_string;
+    tmp_field->org_col_name= empty_string;
+    tmp_field->col_name= name;
     if (maybe_null)
       tmp_field->flags&= ~NOT_NULL_FLAG;
   }

tests/mysql_client_test.c

@@ -11945,6 +11945,73 @@ static void test_bug21726()
 }
 
 
+/*
+  BUG#21635: MYSQL_FIELD struct's member strings seem to misbehave for
+  expression cols
+
+  Check that for MIN(), MAX(), COUNT() only MYSQL_FIELD::name is set
+  to either expression or its alias, and db, org_table, table,
+  org_name fields are empty strings.
+*/
+static void test_bug21635()
+{
+  const char *expr[]=
+  {
+    "MIN(i)", "MIN(i)",
+    "MIN(i) AS A1", "A1",
+    "MAX(i)", "MAX(i)",
+    "MAX(i) AS A2", "A2",
+    "COUNT(i)", "COUNT(i)",
+    "COUNT(i) AS A3", "A3",
+  };
+  const char *query_end;
+  MYSQL_RES *result;
+  MYSQL_FIELD *field;
+  unsigned int field_count, i;
+  int rc;
+
+  DBUG_ENTER("test_bug21635");
+  myheader("test_bug21635");
+
+  query_end= strxmov(query, "SELECT ", NullS);
+  for (i= 0; i < sizeof(expr) / sizeof(*expr) / 2; ++i)
+    query_end= strxmov(query_end, expr[i * 2], ", ", NullS);
+  query_end= strxmov(query_end - 2, " FROM t1 GROUP BY i", NullS);
+  DIE_UNLESS(query_end - query < MAX_TEST_QUERY_LENGTH);
+
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS t1");
+  myquery(rc);
+  rc= mysql_query(mysql, "CREATE TABLE t1 (i INT)");
+  myquery(rc);
+  rc= mysql_query(mysql, "INSERT INTO t1 VALUES (1)");
+  myquery(rc);
+
+  rc= mysql_real_query(mysql, query, query_end - query);
+  myquery(rc);
+
+  result= mysql_use_result(mysql);
+  DIE_UNLESS(result);
+
+  field_count= mysql_field_count(mysql);
+  for (i= 0; i < field_count; ++i)
+  {
+    field= mysql_fetch_field_direct(result, i);
+    printf("%s -> %s ... ", expr[i * 2], field->name);
+    fflush(stdout);
+    DIE_UNLESS(field->db[0] == 0 && field->org_table[0] == 0 &&
+               field->table[0] == 0 && field->org_name[0] == 0);
+    DIE_UNLESS(strcmp(field->name, expr[i * 2 + 1]) == 0);
+    puts("OK");
+  }
+
+  mysql_free_result(result);
+  rc= mysql_query(mysql, "DROP TABLE t1");
+  myquery(rc);
+
+  DBUG_VOID_RETURN;
+}
+
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */
@@ -12172,6 +12239,7 @@ static struct my_tests_st my_tests[]= {
   { "test_bug15613", test_bug15613 },
   { "test_bug20152", test_bug20152 },
   { "test_bug21726", test_bug21726 },
+  { "test_bug21635", test_bug21635 },
   { 0, 0 }
 };