Arrays cannot be nullable ?

[silviucpp]

After I updated clickhouse to last testing version for the following query:

CREATE TABLE example_src(`ck.partition` Date,`ck.created_at` DateTime,`ck.timestamp` DateTime,`arr` Nullable(Array(String)),`customer_id` Nullable(String),`user_action_id` Nullable(Int64),`user_id` Nullable(String)) ENGINE = ReplicatedMergeTree('/var/lib/clickhouse/tables/{shard}/example_src','{replica}',`ck.partition`,`ck.timestamp`,8192);

I get:

Code: 43, e.displayText() = DB::Exception: Nested type Array(String) cannot be inside Nullable type, e.what() = DB::Exception

So this means we cannot have fields of type array that can accept null value ? This was supported before..

Silviu

[alexey-milovidov]

We decided, that for simplicity reasons we need to support either arrays with nullable values or nullable arrays, but not both. And arrays with nullable values seems more useful. Nullable arrays are less needed, because often empty arrays are enough.

This is still subject to change.

[silviucpp]

Hmm, and how do you solve the problem of adding later let's say in a table a row which is array and you want to select records from past where this property was not available ? I mean where new field it's NULL not empty array..

Silviu

[silviucpp]

Hy @alexey-milovidov do you have an opinion on my previous question ?

Silviu

[alexey-milovidov]

This will be more difficult. You could add another field as a flag to indicate older data.
For example, you could have two fields Items Array(String) and HasItems UInt8.
But sometimes it is enough to not differentiate between empty array and undefined array value.

[silviucpp]

Ok then, if the decision that Nullable array are not supported is final then I don't see any option..