%= (Modulo EQUALS) (Transact-SQL)
Divides one number by another and sets a value to the result of the operation. For example, if a variable @x equals 38, then @x %= 5 takes the original value of @x, divides by 5 and sets @x to the remainder of that division (3).
Returns the data type of the argument with the higher precedence. For more information, see Data Type Precedence (Transact-SQL).