一个员工表,有三列

name,category,salary

John, contract,     2000
Joe,   permanent, 2300
Annie,contract,    2050
Jerry, contract,    2550
Tom, permanent, 2340

现在查询表,按照工资从高到低排列,正式工排前面,合同工排后面,如上表,应该输出这样:

 

Tom,permanent, 2340

Joe, permanent,2300

Jerry,contract,  2550

Annie,contract,  2050

John,contract,   2000

SQL语句如何写啊?