Check column existence

Using cqlsh, you can either get the description of all columns and their data types, or discover whether a particular column exists in a table by querying the column’s data.

All columns

The CQLSH command DESCRIBE TABLE shows all the table information, including the columns defined. For example, if the cycling.comments table is defined, the following will return the table definition:

  • CQL

  • Result

DESC cycling.comments;
CREATE TABLE cycling.comments (
    id uuid,
    created_at timestamp,
    comment text,
    commenter text,
    record_id timeuuid,
    PRIMARY KEY (id, created_at)
) WITH CLUSTERING ORDER BY (created_at DESC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'NONE', 'rows_per_partition': '10'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'enabled': 'true', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.DeflateCompressor'}
    AND crc_check_chance = 1.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND speculative_retry = '99PERCENTILE';

Particular column

If a column exists, a SELECT command will return any data stored in the column:

  • CQL

  • Result

SELECT description
FROM cycling.upcoming_calendar
WHERE year = 2015
  AND month = 6;
 description
------------------------------------------------------------------------------
 {'Criterium du Dauphine': 'Easy race', 'Tour du Suisse': 'Hard uphill race'}

(1 rows)

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