There are several ways to define a setting for a user in ClickHouse, depending on the use case and how long you want the setting to be configured. Let's look at a few scenarios...
Configure a setting for a single query
SELECT query can contain a
SETTINGS clause where you can define any number of settings. The settings are only applied for that particular query. For example:
SETTINGS max_threads = 8;
The maximum number of threads will be 8 for this particular query.
Configure a setting for a session
You can define a setting for the lifetime of a client session using a
SET clause. This is handy for ad-hoc testing or for when you want a setting to live for the lifetime of a few queries - but not longer.
SET max_threads = 8;
Configure a setting for a particular user
ALTER USER to define a setting just for one user. For example:
ALTER USER my_user_name SETTINGS max_threads = 8;
You can verify it worked by logging out of your client, logging back in, then use the