Count Number of Users in Cassandra column family?

[Check Peck]

I have a table like this in Cassandra-

    CREATE TABLE DATA_HOLDER (USER_ID TEXT, RECORD_NAME TEXT, RECORD_VALUE
BLOB, PRIMARY KEY (USER_ID, RECORD_NAME));

I want to count distinct USER_ID in my above table? Is there any way I can
do that?

My Cassandra version is:

    [cqlsh 4.1.1 | Cassandra 2.0.10.71 | DSE 4.5.2 | CQL spec 3.1.1 |
Thrift protocol 19.39.0]