I have to add ability to store Nullable data into some column of existing tables, but this tables have ReplicatedMergeTree engine. So I got a question if exists command alter table on cluster modify column... ? And how much it will be cost in time? Thanks!
1 Answers
This is the syntax of the modify query on cluster, it will also update the replicas (but it can take a while).
ALTER TABLE example_table ON CLUSTER example_cluster MODIFY COLUMN IF EXISTS `example_column` Nullable(UInt8)
For the time required to do the operation, it depends on a lot of parameters (the amount of data, the hardware ...), we can't estimate it without more informations.
Usually when we have such modification and we want to ensure that it won't take too much time and that it is working, we make some benchmarks to estimate the time it would take.
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