crackman sas base 1 里面Payroll+Wagerate;
以为这句话等于payroll = payroll +wagerate;
结果在测试里用了自己的理解（故意把last删掉的，方便解读）
data test;
set cxl.dept;
by dept gender;
if  first.gender then payroll =0;
payroll = payroll + wage;

proc print data= test;
run;

得到的结果如下，真心不懂哪里理解错了


[td]

Obs	num	dept	gender	name	wage	payroll
1	1	it	boy	jack	1000	1000
2	2	it	boy	tom	1000	.
3	3	it	girl	rose	500	500
4	4	it	girl	lily	1000	.
5	5	market	boy	tim	50	50
6	6	market	girl	echo	100	100
7	7	market	girl	sq	50	.