Question 1

How do spreadsheet tabs become ClickHouse tables?

Accepted Answer

One spreadsheet is chosen per connection and each grid tab within it becomes its own table, named after the tab. That matches how people actually use spreadsheets, where a single file holds several related but separate things. With headers enabled, row one supplies the column names. Without headers the columns arrive lettered, which works but is rarely what you want to write queries against later.

Question 2

How are column types decided?

Accepted Answer

Conservatively, and everything arrives nullable. Values default to strings unless the column carries a data validation rule identifying it as a number, date or boolean, in which case that type is used, so adding validation rules on the sheet is the reliable way to get proper typing. Doing that before the first sync saves work, since changing a column type afterwards archives the old column under a name carrying its previous type and adds a new one beside it.

Question 3

What breaks if a column gets inserted?

Accepted Answer

Your mappings, silently. Fields are tracked by position, as column A, column B and so on, not by the header text above them. Insert a column in the middle and every mapping after it reads a different source, while the sync carries on writing plausible values under the right names and nothing errors. After any structural edit to the sheet, refresh the schema and check the mappings before trusting the next run.

Question 4

Is a spreadsheet worth putting in ClickHouse at all?

Accepted Answer

As a join target, often yes. A columnar engine built for billions of rows is obviously overkill for four hundred rows of targets, but that is not the point. The value is having the mapping table sit next to the event data you already keep there, so a query attributing behaviour to a segment or a target does not have to reach outside the database. As a standalone dataset, it would not justify the connection on its own.

Question 5

Why load a spreadsheet into a data warehouse?

Accepted Answer

Because spreadsheets hold the numbers no system owns. Targets, account tiering, manual corrections, the mapping between one tool's codes and another's. That data is real and reports depend on it, yet it lives outside every pipeline. ETL brings it in so those values become joinable, and gives you a governed copy with history rather than a link to a file anyone can restructure.

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