How to count unique values in Cassandra databases over a given time frame?

Do you want to get a distinct count of records in Apache Cassandra over a time range? Well tough luck, unlike traditional SQL databases, Cassandra does not support COUNT(DISTINCT ...) queries efficiently, especially across time ranges.

What you want to do is use a command such as the following from within your Cassandra database server and export the output to a file.

cqlsh -u <username> -p '<password>' -e "SELECT id_column FROM <database_name>.<table_name> WHERE timestamp_column > timestamp AND timestamp_column < timestamp ALLOW FILTERING" > id_date.txt

Then you can use a Linux command such as the following to sort out the unique ID values and remove duplicates.

grep -Ev -- '---|id_column|^$' id_date.txt | awk -F'|' '{print $1}' | tr -d ' ' | sort -u > unique_ids.txt

The command works as follows:

grep -Ev -- '---|id_column|^$' Removes headers, separators, and empty lines. awk -F'|' Extracts the first column. tr -d ' ' Removes unwanted spaces. sort -u Sorts the output and removes duplicate IDs.

You can then count those unique IDs with the following command:

cat unique_ids.txt | wc -l

And there you have it... a DISTINCT count of the ID column over your chosen time frame!

#cassandra #databases