Fix for bug #30782: Truncated UNSIGNED BIGINT columns only in SELECT w/ CASE,

JOIN, and ORDER BY

Problem: improper maximum length calculation of the CASE function leads to 
decimal value truncation (storing/retrieving decimal field values).

Fix: accurately calculate maximum length/unsigned flag/decimals parameters 
of the CASE function.

mysql-test/r/case.result

-drop table if exists t1;
+drop table if exists t1, t2;
 select CASE "b" when "a" then 1 when "b" then 2 END;
 CASE "b" when "a" then 1 when "b" then 2 END
 2
@@ -200,3 +200,21 @@ CEMPNUM	EMPMUM1	EMPNUM2
 0.00	0	0.00
 2.00	2	NULL
 DROP TABLE t1,t2;
+End of 4.1 tests
+create table t1 (a int, b bigint unsigned);
+create table t2 (c int);
+insert into t1 (a, b) values (1,4572794622775114594), (2,18196094287899841997),
+(3,11120436154190595086);
+insert into t2 (c) values (1), (2), (3);
+select t1.a, (case t1.a when 0 then 0 else t1.b end) d from t1 
+join t2 on t1.a=t2.c order by d;
+a	d
+1	4572794622775114594
+3	11120436154190595086
+2	18196094287899841997
+select t1.a, (case t1.a when 0 then 0 else t1.b end) d from t1 
+join t2 on t1.a=t2.c where b=11120436154190595086 order by d;
+a	d
+3	11120436154190595086
+drop table t1, t2;
+End of 5.0 tests

mysql-test/t/case.test

@@ -3,7 +3,7 @@
 #
 
 --disable_warnings
-drop table if exists t1;
+drop table if exists t1, t2;
 --enable_warnings
 
 select CASE "b" when "a" then 1 when "b" then 2 END;
@@ -152,4 +152,21 @@ SELECT IFNULL(t2.EMPNUM,t1.EMPNUM) AS CEMPNUM,
   FROM t1 LEFT JOIN t2 ON t1.EMPNUM=t2.EMPNUM;
 
 DROP TABLE t1,t2;
-# End of 4.1 tests
+
+--echo End of 4.1 tests
+
+#
+# #30782: Truncated UNSIGNED BIGINT columns 
+#
+create table t1 (a int, b bigint unsigned);
+create table t2 (c int);
+insert into t1 (a, b) values (1,4572794622775114594), (2,18196094287899841997),
+  (3,11120436154190595086);
+insert into t2 (c) values (1), (2), (3);
+select t1.a, (case t1.a when 0 then 0 else t1.b end) d from t1 
+  join t2 on t1.a=t2.c order by d;
+select t1.a, (case t1.a when 0 then 0 else t1.b end) d from t1 
+  join t2 on t1.a=t2.c where b=11120436154190595086 order by d;
+drop table t1, t2;
+
+--echo End of 5.0 tests

sql/item_cmpfunc.cc

@@ -2530,6 +2530,23 @@ bool Item_func_case::fix_fields(THD *thd, Item **ref)
 }
 
 
+void Item_func_case::agg_str_lengths(Item* arg)
+{
+  set_if_bigger(max_length, arg->max_length);
+  set_if_bigger(decimals, arg->decimals);
+  unsigned_flag= unsigned_flag && arg->unsigned_flag;
+}
+
+
+void Item_func_case::agg_num_lengths(Item *arg)
+{
+  uint len= my_decimal_length_to_precision(arg->max_length, arg->decimals,
+                                           arg->unsigned_flag) - arg->decimals;
+  set_if_bigger(max_length, len); 
+  set_if_bigger(decimals, arg->decimals);
+  unsigned_flag= unsigned_flag && arg->unsigned_flag; 
+}
+
 
 void Item_func_case::fix_length_and_dec()
 {
@@ -2579,15 +2596,22 @@ void Item_func_case::fix_length_and_dec()
   
   max_length=0;
   decimals=0;
-  for (uint i=0 ; i < ncases ; i+=2)
+  unsigned_flag= TRUE;
+  if (cached_result_type == STRING_RESULT)
   {
-    set_if_bigger(max_length,args[i+1]->max_length);
-    set_if_bigger(decimals,args[i+1]->decimals);
-  }
+    for (uint i= 0; i < ncases; i+= 2)
+      agg_str_lengths(args[i + 1]);
     if (else_expr_num != -1)
+      agg_str_lengths(args[else_expr_num]);
+  }
+  else
   {
-    set_if_bigger(max_length,args[else_expr_num]->max_length);
-    set_if_bigger(decimals,args[else_expr_num]->decimals);
+    for (uint i= 0; i < ncases; i+= 2)
+      agg_num_lengths(args[i + 1]);
+    if (else_expr_num != -1) 
+      agg_num_lengths(args[else_expr_num]);
+    max_length= my_decimal_precision_to_length(max_length + decimals, decimals,
+                                               unsigned_flag);
   }
 }
 

sql/item_cmpfunc.h

@@ -753,6 +753,8 @@ class Item_func_case :public Item_func
   void print(String *str);
   Item *find_item(String *str);
   CHARSET_INFO *compare_collation() { return cmp_collation.collation; }
+  void agg_str_lengths(Item *arg);
+  void agg_num_lengths(Item *arg);
 };