ALTER TABLE COLUMN DROP INDEX
Removes an existing index from a column of type symbol.
Removing an index is an atomic, non-blocking, and non-waiting operation. Once the operation is completed, the SQL engine stops using the index for SQL executions, and all its associated files are deleted.
This operation is similar to:
column is a symbol column that has an index before the operation, and no
index afterwards. Readers of the table might be using the index in transaction
A, in the meantime, a writer creates transaction B containing the new version of
the column, minus the index (metadata is set to not have index, and index files
are not copied across to the newer version). When the readers are finished,
QuestDB automatically deletes all the files pertaining to the version of the
column in transaction A (QuestDB uses hardlinks internally to avoid an actual
copy operation of the data files, as they do not change at all).