Bug #17043: Casting trimmed string to decimal loses precision

  Results of string functions were being converted to decimals by first
  being converted to integers, resulting in a loss of precision.

mysql-test/r/func_str.result

@@ -1030,3 +1030,13 @@ c	res
 y,abc	abc
 y,abc	abc
 drop table t1;
+select cast(rtrim('  20.06 ') as decimal(19,2));
+cast(rtrim('  20.06 ') as decimal(19,2))
+20.06
+select cast(ltrim('  20.06 ') as decimal(19,2));
+cast(ltrim('  20.06 ') as decimal(19,2))
+20.06
+select cast(rtrim(ltrim('  20.06 ')) as decimal(19,2));
+cast(rtrim(ltrim('  20.06 ')) as decimal(19,2))
+20.06
+End of 5.0 tests

mysql-test/t/func_str.test

@@ -684,4 +684,11 @@ insert into t1 values ('y,abc'),('y,abc');
 select c, substring_index(lcase(c), @q:=',', -1) as res from t1;
 drop table t1;
 
-# End of 5.0 tests
+#
+# Bug #17043: Casting trimmed string to decimal loses precision
+#
+select cast(rtrim('  20.06 ') as decimal(19,2));
+select cast(ltrim('  20.06 ') as decimal(19,2));
+select cast(rtrim(ltrim('  20.06 ')) as decimal(19,2));
+
+--echo End of 5.0 tests

sql/item_strfunc.cc

@@ -80,6 +80,20 @@ String *Item_str_func::check_well_formed_result(String *str)
 }
 
 
+my_decimal *Item_str_func::val_decimal(my_decimal *decimal_value)
+{
+  DBUG_ASSERT(fixed == 1);
+  char buff[64];
+  String *res, tmp(buff,sizeof(buff), &my_charset_bin);
+  res= val_str(&tmp);
+  if (!res)
+    return 0;
+  (void)str2my_decimal(E_DEC_FATAL_ERROR, (char*) res->ptr(),
+                       res->length(), res->charset(), decimal_value);
+  return decimal_value;
+}
+
+
 double Item_str_func::val_real()
 {
   DBUG_ASSERT(fixed == 1);

sql/item_strfunc.h

@@ -33,6 +33,7 @@ class Item_str_func :public Item_func
   Item_str_func(List<Item> &list) :Item_func(list) {decimals=NOT_FIXED_DEC; }
   longlong val_int();
   double val_real();
+  my_decimal *val_decimal(my_decimal *);
   enum Item_result result_type () const { return STRING_RESULT; }
   void left_right_max_length();
   String *check_well_formed_result(String *str);