Post-merge fix.

mysql-test/r/type_newdecimal.result

@@ -1481,6 +1481,34 @@ drop table t1;
 SELECT 1.000000000000 * 99.999999999998 / 100 a,1.000000000000 * (99.999999999998 / 100) b;
 a	b
 0.9999999999999800000000000000	0.9999999999999800000000000000
+SELECT CAST(1 AS decimal(65,10));
+CAST(1 AS decimal(65,10))
+1.0000000000
+SELECT CAST(1 AS decimal(66,10));
+ERROR 42000: Too big precision 66 specified for column '1'. Maximum is 65.
+SELECT CAST(1 AS decimal(65,30));
+CAST(1 AS decimal(65,30))
+1.000000000000000000000000000000
+SELECT CAST(1 AS decimal(65,31));
+ERROR 42000: Too big scale 31 specified for column '1'. Maximum is 30.
+CREATE TABLE t1 (a int DEFAULT NULL, b int DEFAULT NULL);
+INSERT INTO t1 VALUES (3,30), (1,10), (2,10);
+SELECT a+CAST(1 AS decimal(65,30)) AS aa, SUM(b) FROM t1 GROUP BY aa;
+aa	SUM(b)
+2.000000000000000000000000000000	10
+3.000000000000000000000000000000	10
+4.000000000000000000000000000000	30
+SELECT a+CAST(1 AS decimal(65,31)) AS aa, SUM(b) FROM t1 GROUP BY aa;
+ERROR 42000: Too big scale 31 specified for column '1'. Maximum is 30.
+DROP TABLE t1;
+CREATE TABLE t1 (a int DEFAULT NULL, b int DEFAULT NULL);
+INSERT INTO t1 VALUES (3,30), (1,10), (2,10);
+SET @a= CAST(1 AS decimal);
+SELECT 1 FROM t1 GROUP BY @b := @a, @b;
+1
+1
+1
+DROP TABLE t1;
 End of 5.0 tests
 select cast(143.481 as decimal(4,1));
 cast(143.481 as decimal(4,1))

sql/item_create.cc

@@ -5039,6 +5039,18 @@ create_func_cast(THD *thd, Item *a, Cast_target cast_type,
       my_error(ER_M_BIGGER_THAN_D, MYF(0), "");
       return 0;
     }
+    if (len > DECIMAL_MAX_PRECISION)
+    {
+      my_error(ER_TOO_BIG_PRECISION, MYF(0), len, a->name,
+               DECIMAL_MAX_PRECISION);
+      return 0;
+    }
+    if (dec > DECIMAL_MAX_SCALE)
+    {
+      my_error(ER_TOO_BIG_SCALE, MYF(0), dec, a->name,
+               DECIMAL_MAX_SCALE);
+      return 0;
+    }
     res= new (thd->mem_root) Item_decimal_typecast(a, len, dec);
     break;
   }