What is the advantage of cassandra database? : Could you let me know why do we use the Cassandra database?

We cannot search Cassandra tables with other than those in the primary key or clustering columns.

For example, if my primary key is 'a' and clustering columns are 'b' and 'c'.

I can only use the following in where condition.

    select * from table where a = 1 and b = 2 and c = 3

Or there any other queries that I can use with where?

I want to use 

    select * from table where a=1

and 

    select * from table where a = 1 and b = 2 and c = 3 and d = 4

Is that possible?

If not, then why people chose to use Cassandra if it is not serving this minimum request.