Some questions about Cassandra where clause

0
votes

I am reading A deep look at the CQL WHERE clause. I am confused by several statements, so I posted 5 questions (Q1 - Q5). Any comments welcomed. Thanks

Q1: What does Secondary index queries mean? What does the query is using a secondary index mean?

I think secondary index queries==the query which is using a secondary index.

But Secondary index queries means queries on the table where secondary index exists OR the queried columns are all indexed OR at least one column among all queried columns is indexed?

Single column slice restrictions are allowed only on the last clustering column being restricted.

Q2: Single column slice restrictions mean >, >=, <=, <?

Direct queries on secondary indices support only =, CONTAINS or CONTAINS KEY restrictions.

Q3: The indexed columns can be restricted only by =, CONTAINS, and CONTAINS KEY?

CONTAINS and CONTAINS KEY restrictions can only be used on collections when the query is using a secondary index.

Q4: CONTAINS can be used on any non-indexed clustering column? Buy when one column is secondary indexed, CONTAINS can only be used on this column when this column is collections type?

Regular columns can be restricted by =, >, >=, <= and <, CONTAINS or CONTAINS KEY restrictions if the query is a secondary index query. IN restrictions are not supported.

Q5: What does Regular columns mean? Always Single column slice restrictions are allowed only on the last clustering column being restricted.. If one column is secondary indexed, =, >, >=, <= and <, CONTAINS or CONTAINS KEY restrictions (but not IN) can be restricted on this column, even if it is not last clustering column?

1
cassandracqlcql3

1 Answers

0
votes

Q1: Secondary index is all the example where they use 'CREATE INDEX'.

Q2: Yes, all of those inequality operators produce a slice of the query.

Q3: Yes, essentially CONTAINS will look inside a collection and look for that particular item. It only works if the column has a secondary index otherwise Cassandra would have to scan every collection to check.

Q4/5: Questions are a bit confusing. Regular columns in this context will be non-partition key columns.