2 logics (Where also and Subsetting IF)

1. if City =: 'B';

It selects the observation if the data values of CITY variable starts with 'B' character (i.e,'B' at the first position in the City variable value).
Egg: City= "Bangalore", "Bahrain" etc., but not "bombay"

2. Where also Salary > 10000;

In general we cant use 2 where statements in a single data step. Means, if you executed a datastep which contains 2 where statements, then only the 2nd where statement will work. In this case you need to use where also statement instead of 2nd where statement.

Before:
data b;
set a;
where gender='M';
where salary > 10000;
run;

After:
data b;
set a;
where gender='M';
where also salary > 10000;
run;