Bug#37662 nested if() inside sum() is parsed in exponential time

      
min() and max() functions are implemented in MySQL as macros.
This means that max(a,b) is expanded to: ((a) > (b) ? (a) : (b))
Note how 'a' is quoted two times.
Now imagine 'a' is a recursive function call that's several 10s of levels deep.
And the recursive function does max() with a function arg as well to dive into
recursion.
This means that simple function call can take most of the clock time.
Identified and fixed several such calls to max()/min() : including the IF() 
sql function implementation.

mysql-test/r/func_if.result:
  Bug#37662 test case
mysql-test/t/func_if.test:
  Bug#37662 test case
sql/item.cc:
  Bug#37662 don't call expensive functions as arguments to min/max
sql/item_cmpfunc.cc:
  Bug#37662 don't call expensive functions as arguments to min/max
sql/item_func.cc:
  Bug#37662 don't call expensive functions as arguments to min/max

1 files changed, 8 insertions, 4 deletions

diff --git a/sql/item.cc b/sql/item.cc
index bf447581afa..a5c88f55487 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -429,8 +429,11 @@ uint Item::decimal_precision() const
   Item_result restype= result_type();
 
   if ((restype == DECIMAL_RESULT) || (restype == INT_RESULT))
-    return min(my_decimal_length_to_precision(max_length, decimals, unsigned_flag),
-               DECIMAL_MAX_PRECISION);
+  {
+    uint prec= 
+      my_decimal_length_to_precision(max_length, decimals, unsigned_flag);
+    return min(prec, DECIMAL_MAX_PRECISION);
+  }
   return min(max_length, DECIMAL_MAX_PRECISION);
 }
 
@@ -6838,8 +6841,9 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
   if (Field::result_merge_type(fld_type) == DECIMAL_RESULT)
   {
     decimals= min(max(decimals, item->decimals), DECIMAL_MAX_SCALE);
-    int precision= min(max(prev_decimal_int_part, item->decimal_int_part())
-                       + decimals, DECIMAL_MAX_PRECISION);
+    int item_int_part= item->decimal_int_part();
+    int item_prec = max(prev_decimal_int_part, item_int_part) + decimals;
+    int precision= min(item_prec, DECIMAL_MAX_PRECISION);
     unsigned_flag&= item->unsigned_flag;
     max_length= my_decimal_precision_to_length(precision, decimals,
                                                unsigned_flag);