Change column name in a table in Clickhouse

Question

Is there any way to ALTER a table and change the column name in clickhouse? I only found to change tha table name but not for an individual column in a straight forward way.

Thanks.

Answer 1

The feature has been introduced here into v20.4.

ALTER TABLE table1 RENAME COLUMN old_name TO new_name

You can also rename multiple columns at on:

ALTER TABLE table1 
    RENAME COLUMN old_name1 TO new_name1, 
    RENAME COLUMN old_name2 TO new_name2

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Old answer:

ClickHouse doesn't have that feature yet.

Implementation is not trivial, because ALTERs that changing columns are processed outside of usual replication queue, and adding rename without reworking of ALTERs will introduce race conditions in replicated tables.

https://github.com/yandex/ClickHouse/issues/146#issuecomment-255631384

As @Slash said, the solution for now is to create new table and

INSERT INTO `new_table` SELECT * FROM `old_table`

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Do not forget that column aliasing won't work there (AS).

INSERT INTO `new_table` SELECT a, b AS c, c AS b FROM `old_table`

That will still insert a into first column, b into second column and c into third column. AS has no effect there.

Answer 2

You can try use CREATE TABLE new_table with another field name and run INSERT INTO new_table SELECT old_field AS new_field FROM old_table