Building Complex Data Model using Nested Data in BigQuery

was talking to someone I know on twitter, and got this cryptic reply

I have a vague idea of how to nest two tables, specially Header/Details, it is very easy to conceptualize but I never really understood Json format or how to get multiple levels.

Building a Nested Table

Just for fun I tried to convert this Data Model, a typical Multi fact Star Schema ( apparently it is called galaxy Schema)

I am not going to share the SQL Query that converted those 3 facts Table to 1 Nested Table ( because it is probably horrible), it took me some time to get a mental image how to stack the common dimensions first, and started nesting the common values at lower level, anyway I end up with this schema

And here is a Preview

Querying Nested Table

Front end tools don’t support nested Data by default, you have to flattened it first using SQL , Exception Data Studio but you have to be careful of this bug

A recent interesting development, Looker out of nowhere introduced a New Open Source Analytics Language called “Malloy” , and it has a first class support for nested Data, see example here

It is just a fun exercise, BigQuery support Star Schema just fine, but according to people who work with Big Data, let’s say 2 billion rows and such, not doing join is extremely Faster and cheaper, and apparently it is easier to transfer Data, after all moving one Table is easier than moving three.

Now even if all what you do is Star Schema, it is fruitful to learn other approaches, turn out Json format is useful aft all 🙂


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