Fix for bug #8429 (FORMAT returns incorrect result)

mysql-test/r/func_math.result:
  test result ixed
mysql-test/t/func_math.test:
  test case added
sql/item_strfunc.cc:
  Item_func_format::val_str now handles 'decimal' and 'double' values in
  different way

mysql-test/r/func_math.result

@@ -130,3 +130,16 @@ Warnings:
 Note	1003	select degrees(pi()) AS `degrees(pi())`,radians(360) AS `radians(360)`
 select rand(rand);
 ERROR 42S22: Unknown column 'rand' in 'field list'
+create table t1 (col1 int, col2 decimal(60,30));
+insert into t1 values(1,1234567890.12345);
+select format(col2,7) from t1;
+format(col2,7)
+1,234,567,890.1234500
+select format(col2,8) from t1;
+format(col2,8)
+1,234,567,890.12345000
+insert into t1 values(7,1234567890123456.12345);
+select format(col2,6) from t1 where col1=7;
+format(col2,6)
+1,234,567,890,123,456.123450
+drop table t1;

mysql-test/t/func_math.test

@@ -67,3 +67,15 @@ explain extended select degrees(pi()),radians(360);
 
 --error 1054
 select rand(rand);
+
+#
+# Bug #8459 (FORMAT returns incorrect result)
+#
+create table t1 (col1 int, col2 decimal(60,30));
+insert into t1 values(1,1234567890.12345);
+select format(col2,7) from t1;
+select format(col2,8) from t1;
+insert into t1 values(7,1234567890123456.12345);
+select format(col2,6) from t1 where col1=7;
+drop table t1;
+

sql/item_strfunc.cc

@@ -1668,14 +1668,28 @@ Item_func_format::Item_func_format(Item *org,int dec) :Item_str_func(org)
 
 String *Item_func_format::val_str(String *str)
 {
+  uint32 length, str_length ,dec;
+  int diff;
   DBUG_ASSERT(fixed == 1);
+  dec= decimals ? decimals+1 : 0;
+
+  if (args[0]->result_type() == DECIMAL_RESULT ||
+      args[0]->result_type() == INT_RESULT)
+  {
+    my_decimal dec_val, rnd_dec, *res;
+    res= args[0]->val_decimal(&dec_val);
+    my_decimal_round(E_DEC_FATAL_ERROR, res, decimals, false, &rnd_dec);
+    my_decimal2string(E_DEC_FATAL_ERROR, &rnd_dec, 0, 0, 0, str);
+    str_length= str->length();
+    if (rnd_dec.sign())
+      str_length--;
+  }
+  else
+  {
     double nr= args[0]->val_real();
-  uint32 length,str_length,dec;
-  int diff;
     if ((null_value=args[0]->null_value))
       return 0; /* purecov: inspected */
     nr= my_double_round(nr, decimals, FALSE);
-  dec= decimals ? decimals+1 : 0;
     /* Here default_charset() is right as this is not an automatic conversion */
     str->set(nr,decimals, default_charset());
     if (isnan(nr))
@@ -1683,7 +1697,7 @@ String *Item_func_format::val_str(String *str)
     str_length=str->length();
     if (nr < 0)
       str_length--;				// Don't count sign
-
+  }
   /* We need this test to handle 'nan' values */
   if (str_length >= dec+4)
   {