how to do subtraction in mysql

i want to subtract 1 from a variable who is stored in my table in mysql

i do it by this query

UPDATE table SET  var = var -1

but when i do it

0 - 1 = -1

but mysql do

0 - 1 = 9223开发者_开发技巧372036854775807 when i set in bigint when i set it to int property then he do

0 -1 = 2147483647

what i do to get

0 - 1 = -1

You need to choose a different (signed) data type that allows storing negative values.

look here for some background :

• http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html
• Signed versus Unsigned Integers