Sep 22, 2021

ClickHouse tips #11: Best way to get query types

A fast and simple solution to know the types returned by a query

There are situations when we might want to retrieve the type of a query, function, aggregation, etc in ClickHouse. This information could be really important when we want to identify and debug an issue.

Checking in the docs of ClickHouse, it seems like using toTypeName(x) would provide all that we need.

But there is a catch. For toTypeName(x) to return the type, first, it will need to execute the query. This can lead to a long response time and we might get duplicated results that we do not care about like in the following example.

So, can we find a better solution? Yes, using DESCRIBE.

DESCRIBE will return the type after evaluating the query, without execution, and will return only one entry per column. Resulting in an incredible performance boost and more simple solution

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