Fix for BUG#6825: When calculating Item_func_neg::max_length, add 1 for '-'.

For numeric constants we only need to add, since the parser doesn't produce 
negative numbers. 
For strings we only add (we actually could substract 1 if given string is a constant 
and it has '-number' form but we're not doing that because 
 * we set max_length bigger then necessary in other cases as well.  
 * the current solution is simpler and safer (bigger max_length is better then cutting out)


mysql-test/r/func_concat.result:
  Test for BUG#6825
mysql-test/r/metadata.result:
  Ajusted results according to fix of bug BUG#6825:length(-1) = 2 , not 1
mysql-test/t/func_concat.test:
  Test for BUG#6825

1 files changed, 16 insertions, 0 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index 2d939f47716..413000f9d1b 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -775,9 +775,25 @@ longlong Item_func_neg::val_int()
 
 void Item_func_neg::fix_length_and_dec()
 {
+  enum Item_result arg_result= args[0]->result_type();
+  enum Item::Type  arg_type= args[0]->type();
   decimals=args[0]->decimals;
   max_length=args[0]->max_length;
   hybrid_type= REAL_RESULT;
+  
+  /*
+    We need to account for added '-' in the following cases:
+    A) argument is a real or integer positive constant - in this case 
+    argument's max_length is set to actual number of bytes occupied, and not 
+    maximum number of bytes real or integer may require. Note that all 
+    constants are non negative so we don't need to account for removed '-'.
+    B) argument returns a string.
+  */
+  if (arg_result == STRING_RESULT || 
+      (arg_type == REAL_ITEM && ((Item_real*)args[0])->value >= 0) ||
+      (arg_type == INT_ITEM && ((Item_int*)args[0])->value > 0))
+    max_length++;
+
   if (args[0]->result_type() == INT_RESULT)
   {
     /*