ALTER TABLE DROP COLUMN

Drops a column from an existing table.

Before the operation can proceed, any current transactions are committed, regardless of the success or failure of the DROP operation. Dropping a column does not lock the table for reading and does not wait on any reads to finish.

Dropping columns will also attempt to remove files belonging to the column from all partitions, thus freeing up disk space immediately. If this is not immediately possible on Windows, the file remove operation is postponed until files are released by all threads. The logical drop column will succeed on Windows in presence of active readers.

caution

Use DROP COLUMN with care as QuestDB cannot recover data from dropped columns!

Syntax#

Flow chart showing the syntax of the ALTER TABLE keyword

Example#

The following example deletes the column called comment from the table ratings

Dropping a column

ALTER TABLE ratings DROP COLUMN movieId;