Bug #45262: Bad effects with CREATE TABLE and DECIMAL

 
Using DECIMAL constants with more than 65 digits in CREATE 
TABLE ... SELECT led to bogus errors in release builds or 
assertion failures in debug builds. 
 
The problem was in inconsistency in how DECIMAL constants and 
fields are handled internally. We allow arbitrarily long 
DECIMAL constants, whereas DECIMAL(M,D) columns are limited to 
M<=65 and D<=30. my_decimal_precision_to_length() was used in 
both Item and Field code and truncated precision to 
DECIMAL_MAX_PRECISION when calculating value length without 
adjusting precision and decimals. As a result, a DECIMAL 
constant with more than 65 digits ended up having length less 
than precision or decimals which led to assertion failures. 
 
Fixed by modifying my_decimal_precision_to_length() so that 
precision is truncated to DECIMAL_MAX_PRECISION only for Field 
object which is indicated by the new 'truncate' parameter. 
 
Another inconsistency fixed by this patch is how DECIMAL 
constants and expressions are handled for CREATE ... SELECT. 
create_tmp_field_from_item() (which is used for constants) was 
changed as a part of the bugfix for bug #24907 to handle long 
DECIMAL constants gracefully. Item_func::tmp_table_field() 
(which is used for expressions) on the other hand was still 
using a simplistic approach when creating a Field_new_decimal 
from a DECIMAL expression. 

mysql-test/r/type_newdecimal.result:
  Added a test case for bug #45262.
mysql-test/t/type_newdecimal.test:
  Added a test case for bug #45262.
sql/item.cc:
  Use the new 'truncate' parameter in 
  my_decimal_precision_to_length().
sql/item_cmpfunc.cc:
  Use the new 'truncate' parameter in 
  my_decimal_precision_to_length().
sql/item_func.cc:
  1. Use the new 'truncate' parameter in 
  my_decimal_precision_to_length().
  
  2. Do not truncate decimal precision to DECIMAL_MAX_PRECISION
  for additive expressions involving long DECIMAL constants.
  
  3. Fixed an incosistency in how DECIMAL constants and 
  expressions are handled for CREATE ... SELECT.
sql/item_func.h:
  Use the new 'truncate' parameter in 
  my_decimal_precision_to_length().
sql/item_sum.cc:
  Use the new 'truncate' parameter in 
  my_decimal_precision_to_length().
sql/my_decimal.h:
  Do not truncate precision to DECIMAL_MAX_PRECISION
  when calculating length in 
  my_decimal_precision_to_length() if 'truncate' parameter
  is FALSE.
sql/sql_select.cc:
  1. Use the new 'truncate' parameter in 
  my_decimal_precision_to_length().
  
  2. Use a more correct logic when adjusting value's length.

1 files changed, 54 insertions, 17 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index 6193ab285f2..7f7f79480ca 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -447,11 +447,46 @@ Field *Item_func::tmp_table_field(TABLE *t_arg)
     res= make_string_field(t_arg);
     break;
   case DECIMAL_RESULT:
-    res= new Field_new_decimal(my_decimal_precision_to_length(decimal_precision(),
-                                                              decimals,
-                                                              unsigned_flag),
-                               maybe_null, name, t_arg, decimals, unsigned_flag);
+  {
+    uint8 dec= decimals;
+    uint8 intg= decimal_precision() - dec;
+    uint32 len= 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)
+    {
+      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.
+      */
+
+      const int required_length=
+        my_decimal_precision_to_length(intg + dec, dec,
+                                                     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;
+    }
+
+    res= new Field_new_decimal(len, maybe_null, name,
+                               t_arg, dec, unsigned_flag);
     break;
+  }
   case ROW_RESULT:
   default:
     // This case should never be chosen
@@ -540,8 +575,8 @@ void Item_func::count_decimal_length()
     set_if_smaller(unsigned_flag, args[i]->unsigned_flag);
   }
   int precision= min(max_int_part + decimals, DECIMAL_MAX_PRECISION);
-  max_length= my_decimal_precision_to_length(precision, decimals,
-                                             unsigned_flag);
+  max_length= my_decimal_precision_to_length_no_truncation(precision, decimals,
+                                                           unsigned_flag);
 }
 
 
@@ -1158,16 +1193,15 @@ void Item_func_additive_op::result_precision()
   decimals= max(args[0]->decimals, args[1]->decimals);
   int arg1_int= args[0]->decimal_precision() - args[0]->decimals;
   int arg2_int= args[1]->decimal_precision() - args[1]->decimals;
-  int est_prec= max(arg1_int, arg2_int) + 1 + decimals;
-  int precision= min(est_prec, DECIMAL_MAX_PRECISION);
+  int precision= max(arg1_int, arg2_int) + 1 + decimals;
 
   /* Integer operations keep unsigned_flag if one of arguments is unsigned */
   if (result_type() == INT_RESULT)
     unsigned_flag= args[0]->unsigned_flag | args[1]->unsigned_flag;
   else
     unsigned_flag= args[0]->unsigned_flag & args[1]->unsigned_flag;
-  max_length= my_decimal_precision_to_length(precision, decimals,
-                                             unsigned_flag);
+  max_length= my_decimal_precision_to_length_no_truncation(precision, decimals,
+                                                           unsigned_flag);
 }
 
 
@@ -1270,7 +1304,8 @@ void Item_func_mul::result_precision()
   decimals= min(args[0]->decimals + args[1]->decimals, DECIMAL_MAX_SCALE);
   uint est_prec = args[0]->decimal_precision() + args[1]->decimal_precision();
   uint precision= min(est_prec, DECIMAL_MAX_PRECISION);
-  max_length= my_decimal_precision_to_length(precision, decimals,unsigned_flag);
+  max_length= my_decimal_precision_to_length_no_truncation(precision, decimals,
+                                                           unsigned_flag);
 }
 
 
@@ -1326,8 +1361,8 @@ void Item_func_div::result_precision()
   else
     unsigned_flag= args[0]->unsigned_flag & args[1]->unsigned_flag;
   decimals= min(args[0]->decimals + prec_increment, DECIMAL_MAX_SCALE);
-  max_length= my_decimal_precision_to_length(precision, decimals,
-                                             unsigned_flag);
+  max_length= my_decimal_precision_to_length_no_truncation(precision, decimals,
+                                                           unsigned_flag);
 }
 
 
@@ -2013,8 +2048,9 @@ void Item_func_round::fix_length_and_dec()
 
     precision-= decimals_delta - length_increase;
     decimals= min(decimals_to_set, DECIMAL_MAX_SCALE);
-    max_length= my_decimal_precision_to_length(precision, decimals,
-                                               unsigned_flag);
+    max_length= my_decimal_precision_to_length_no_truncation(precision,
+                                                             decimals,
+                                                             unsigned_flag);
     break;
   }
   default:
@@ -2249,8 +2285,9 @@ void Item_func_min_max::fix_length_and_dec()
     }
   }
   else if ((cmp_type == DECIMAL_RESULT) || (cmp_type == INT_RESULT))
-    max_length= my_decimal_precision_to_length(max_int_part+decimals, decimals,
-                                            unsigned_flag);
+    max_length= my_decimal_precision_to_length_no_truncation(max_int_part +
+                                                             decimals, decimals,
+                                                             unsigned_flag);
   cached_field_type= agg_field_type(args, arg_count);
 }