Bug #45261 : Crash, stored procedure + decimal

Bug #48370  Absolutely wrong calculations with GROUP BY and
  decimal fields when using IF

Added the test cases in the above two bugs for regression
testing.
Added additional tests that demonstrate a incomplete fix.
Added a new factory method for Field_new_decimal to 
create a field from an (decimal returning) Item.
In the new method made sure that all the precision and 
length variables are capped in a proper way. 
This is required because Item's can have larger precision
than the decimal fields and thus need to be capped when
creating a field based on an Item type.
Fixed the wrong typecast to Item_decimal.

1 files changed, 1 insertions, 40 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 18fc3b20748..569d8183ab6 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -9466,47 +9466,8 @@ static Field *create_tmp_field_from_item(THD *thd, Item *item, TABLE *table,
     new_field->set_derivation(item->collation.derivation);
     break;
   case DECIMAL_RESULT:
-  {
-    uint8 dec= item->decimals;
-    uint8 intg= ((Item_decimal *) item)->decimal_precision() - dec;
-    uint32 len= item->max_length;
-
-    /*
-      Trying to put too many digits overall in a DECIMAL(prec,dec)
-      will always throw a warning. We must limit dec to
-      DECIMAL_MAX_SCALE however to prevent an assert() later.
-    */
-
-    if (dec > 0)
-    {
-      signed int overflow;
-
-      dec= min(dec, DECIMAL_MAX_SCALE);
-
-      /*
-        If the value still overflows the field with the corrected dec,
-        we'll throw out decimals rather than integers. This is still
-        bad and of course throws a truncation warning.
-        +1: for decimal point
-      */
-
-      const int required_length=
-        my_decimal_precision_to_length(intg + dec, dec,
-                                                     item->unsigned_flag);
-
-      overflow= required_length - len;
-
-      if (overflow > 0)
-        dec= max(0, dec - overflow);            // too long, discard fract
-      else
-        /* Corrected value fits. */
-        len= required_length;
-    }
-
-    new_field= new Field_new_decimal(len, maybe_null, item->name,
-                                     dec, item->unsigned_flag);
+    new_field= Field_new_decimal::create_from_item(item);
     break;
-  }
   case ROW_RESULT:
   default:
     // This case should never be choosen