I have a cassandra database and a family of columns with columns (secondary keys) A, B, C. I need to select all rows from it, but the filter rows with an empty column B. Can this be done using CQL? Or is it possible to simply select rows with an empty column (in cql, secondary keys can only be filtered by the exact value)?
No, this is currently not possible. Filtering must be done on the client side.
If this is a type of query that you know you need in advance, I recommend maintaining the row index without column B.