Why am I getting a 'Nullable Array' table error?

Use case

"I'm setting up a Database on Velvet, but this table won't connect:"

TLDR

• ClickHouse doesn't support Nullable Arrays
• It does support Arrays that contain nulls
• To resolve: Uncheck isArray, or make it non-nullable, or don't include that column

Solution

When you connect a database to Velvet, we let you map your tables and mark as isArray for more accurate results. ClickHouse does not support Nullable Arrays, but it does support Arrays that contain nulls. So if you see the error Nested type Array(String) cannot be inside Nullable type. 43 when connecting a table, there are a few easy solutions:

1. Uncheck isArray in Velvet's database table connection UI.
2. Don't include this column in the Velvet sync.
3. If you need this particular array structure, you can make it non-nullable.

Suggested reading on this topic

• Github issue from ClickHouse "Arrays cannot be nullable ? #1062"
• Array documentation from ClickHouse.

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