Change MySQL engine configuration when the mysql is not accessable

[shwangdev]

I have a database in clickhouse which is using MySQL engine. However, for some reason the IP of that mysql server was changed. I can not drop the db in clickhouse , cause it reports can not access the old mysql ip.
So, how can I change the db engine configuration in clickhouse?

[tavplubix]

Reopen, because #28054 was reverted (so we don't forget to fix the test and merge it again)

[baxitashraf]

Yes, you can change the Table engine.

CREATE TABLE example_table (id UInt32, data Float64)
ENGINE=MergeTree() ORDER BY id;

Insert into example_table values(1,1), (1,1), (2,1);

CREATE TABLE example_table1 (id UInt32, data Float64)
ENGINE=SummingMergeTree() ORDER BY id;

-- this does not copy any data (instant & almost free command)
alter table example_table1 attach partition tuple() from example_table;

optimize table example_table1 final;