How does one count/sum data values in a column?

Count/sum FIX values:

Use this simple query to count the number of data values in a column:

select my_table_column, count(*)
from   my_table
group  by my_table_column;

A more sophisticated example...

select dept, sum(  decode(sex,'M',1,0)) MALE,
          sum(  decode(sex,'F',1,0)) FEMALE,
          count(decode(sex,'M',1,'F',1)) TOTAL
from my_emp_table
group by dept;

Count/sum RANGES of data values in a column:

A value x will be between values y and z if GREATEST(x, y) = LEAST(x, z). Look at this example:

select f2,
    sum(decode(greatest(f1,59), least(f1,100), 1, 0)) "Range 60-100",
    sum(decode(greatest(f1,30), least(f1, 59), 1, 0)) "Range 30-59",
    sum(decode(greatest(f1, 0), least(f1, 29), 1, 0)) "Range 00-29"
from   my_table
group  by f2;

For equal size ranges it might be easier to calculate it with DECODE(TRUNC(value/range), 0, rate_0, 1, rate_1, ...). Eg.

select ename "Name", sal "Salary",
    decode( trunc(f2/1000, 0), 0, 0.0,
                               1, 0.1,
                               2, 0.2,
                               3, 0.31) "Tax rate"
from   my_table;