Questions around 2: Concept: Loading Data  [Solved]

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RafaelKnuth
Posts: 4
Joined: Fri May 18, 2018 8:07 pm

Questions around 2: Concept: Loading Data

Postby RafaelKnuth » Fri May 18, 2018 8:21 pm

I am confused by a couple things right from the start:

p. 8: Why do I not need to load the dim tables, but just the fact queries? Common sense is telling me, that I should load the dim tables + the fact table and then make one to many joints from dim (one) to fact (many). Or am I mising something here?
p. 11: When joining tables, the one to many relationships are automatically created, no matter in which order I join my tables. It's always Calendar(one) to Sales(many), Customers(one) to Sales (many). It makes sense to me, and I cannot comprehend why I am supposed to join my tables the other way round. Just doesn't make sense to me. One Sales record to many Dates, Customers etc.
p. 15: When making changes to a table that is already loaded, I am getting an error message saying that the table was created in Power Query and I should modify it here. That makes sense to m (because I was supposed to load ony queries from the sample data on p.8). That said, I am assuming that if I had loaded the dim tables in the first place, I shouldbe able to do the modificatinos in my data model.

I am fairly new to the game of data analytics, and the above is just confusing and not logical to me, but like I said - I'm am a rookie, and I might not see & comprehend the bigger picture yet. Thanks in advance!

RamanaV
Posts: 14
Joined: Thu Oct 19, 2017 12:57 pm

Re: Questions around 2: Concept: Loading Data  [Solved]

Postby RamanaV » Sat May 19, 2018 2:46 pm

Hi,

Here are some clarifications:
1. In the data model you will have lookup tables (dim tables) and data tables (fact tables).
In the sample AdventureWorks database, the tables are cleaned and shaped for a direct load into your data model.
However, it may not be the case when you get data from else where. In such cases you have to determine what lookup tables you will have, what columns each of the lookup tables will have, and what is the column in each lookup table that will have unique values (key column). The key columns and the transactions data must be in the data table. Then you need to connect the tables defining the one-to-many relationships. When you get data from a database, it might happen that some relationships already exist. But you need to make sure that they are the right relationships.
2. When joining tables, whatever order you connect the tables, it is always a one-to-many relationship (lookup table on the one-side and data table on the many-side) and you can observe that with the '1' and '*' at the ends of the relationship line. It is never one sales record to many dates, and it is always many sales records to one date. Matt prefers to join the tables from data table to lookup tables.
3. If you edit the tables in Power Query and then load into the data model, you should always do any modifications later in Power Query only. Even otherwise, it is always better to load and shape data in Power Query as it is the right tool for the purpose.

Data Modelling is not easy to learn and the only way you can become an expert is by practice. Do every solved worked through example yourself, and then solve the other exercises, verify your answers given in the book. If you have any doubt, reread the lesson. Move to the next lesson only when you think you understood the present lesson.

And, if you are finding it difficult to start on the DAX journey by yourself, you can enroll to Matt's "Supercharge Power BI" Online Training Course which is a guided course with weekly live Q&A sessions with Matt (for 5 weeks).

Hope this information helps.

RafaelKnuth
Posts: 4
Joined: Fri May 18, 2018 8:07 pm

Re: Questions around 2: Concept: Loading Data

Postby RafaelKnuth » Sat May 19, 2018 5:20 pm

Ramana,

thank you so much for the clarification. I've only struggled a bit at the very beginning of the book, I am halfway through now - and I truly enjoy learning DAX as I find it very powerful.

Best,

Rafael


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