returns incorrect result with large decimal value" 
 
For the DIV operator, neither operands nor result were checked 
for integer overflows. 
 
This patch changes the DIV behavior for non-integer operands as 
follows: if either of the operands has a non-integer type, 
convert both operands to the DECIMAL type, then calculate the 
division using DECIMAL arithmetics. Convert the resulting 
DECIMAL value into BIGINT [UNSIGNED] if it fits into the 
corresponding range, or throw an 'out of range' error 
otherwise. 

mysql-test/r/func_math.result:
  Added a test case for bug #8457.
  Fixed results for a test case depending on the wrong behavior.
mysql-test/r/type_varchar.result:
  Fixed results for a test case depending on the wrong behavior.
mysql-test/t/func_math.test:
  Added a test case for bug #8457.
sql/item_func.cc:
  If either of the operands has a non-integer type, convert both 
  operands to the DECIMAL type, then calculate the division using 
  DECIMAL arithmetics. Convert the resulting DECIMAL value into 
  BIGINT [UNSIGNED] if it fits into the corresponding range, or 
  throw an 'out of range' error otherwise.