different (simpler and more compatible) fix for bug#4046

mysql-test/r/type_decimal.result

@@ -363,6 +363,13 @@ CREATE TABLE t1 (a_dec DECIMAL(-2,1));
 Too big column length for column 'a_dec' (max = 255). Use BLOB instead
 CREATE TABLE t1 (a_dec DECIMAL(-1,1));
 Too big column length for column 'a_dec' (max = 255). Use BLOB instead
+CREATE TABLE t1 (a_dec DECIMAL(0,11));
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a_dec` decimal(12,11) default NULL
+) TYPE=MyISAM
+DROP TABLE t1;
 create table t1(a decimal(7,3));
 insert into t1 values ('1'),('+1'),('-1'),('0000000001'),('+0000000001'),('-0000000001'),('10'),('+10'),('-10'),('0000000010'),('+0000000010'),('-0000000010'),('100'),('+100'),('-100'),('0000000100'),('+0000000100'),('-0000000100'),('1000'),('+1000'),('-1000'),('0000001000'),('+0000001000'),('-0000001000'),('10000'),('+10000'),('-10000'),('0000010000'),('+0000010000'),('-0000010000'),('100000'),('+100000'),('-100000'),('0000100000'),('+0000100000'),('-0000100000'),('1000000'),('+1000000'),('-1000000'),('0001000000'),('+0001000000'),('-0001000000'),('10000000'),('+10000000'),('-10000000'),('0010000000'),('+0010000000'),('-0010000000'),('100000000'),('+100000000'),('-100000000'),('0100000000'),('+0100000000'),('-0100000000'),('1000000000'),('+1000000000'),('-1000000000'),('1000000000'),('+1000000000'),('-1000000000');
 select * from t1;

mysql-test/t/type_decimal.test

@@ -240,6 +240,9 @@ CREATE TABLE t1 (a_dec DECIMAL(-1,0));
 CREATE TABLE t1 (a_dec DECIMAL(-2,1));
 --error 1074
 CREATE TABLE t1 (a_dec DECIMAL(-1,1));
+CREATE TABLE t1 (a_dec DECIMAL(0,11));
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
 
 #
 #  Zero prepend overflow bug

sql/sql_parse.cc

@@ -3157,7 +3157,10 @@ bool add_field_to_list(char *field_name, enum_field_types type,
     break;
   case FIELD_TYPE_DECIMAL:
     if (!length)
-      new_field->length= 10;			// Default length for DECIMAL
+      if (new_field->length= new_field->decimals)
+        new_field->length++;
+      else
+        new_field->length=10;                   // Default length for DECIMAL
     if (new_field->length < MAX_FIELD_WIDTH)	// Skip wrong argument
     {
       new_field->length+=sign_len;