Database Reference
In-Depth Information
Warning: Visualization Tools Can Run a Lot
of Queries
In Tableau, when you drag and drop a field to indicate you want it to
represent the rows of your chart, or change the aggregation from
SUM()
to
COUNT()
, it issues a query. If you tweak the parameters a lot,
it can cause you to run a lot of queries. If you run a lot of queries over a
large table, it is going to get expensive.
Other Visualization tools such as BIME, have the same issue. They
trade off ease of use for understanding exactly which queries are going
to be executed and when. Visualization tools frequently issue queries to
get statistics about certain columns, or in response to interactions you
make in the UI.
The automatic caching that BigQuery does can help out here—if a query
has already been issued within the last 24 hours, the cached results will
be retuned rather than running a separate query. That said, if you have
billions of rows in your table, you should know that every time you
tweak something it might cost you money.
Connecting Tableau to Your BigQuery Tables
Tableau has built-in support for BigQuery; to connect to a BigQuery table,
follow these steps:
1. Open Tableau to a blank workspace; then click Connect to Data. This
opens a menu that lists the different types of data sources Tableau can
communicate with.
2. Under the On a Server menu, select Google BigQuery. This pops up a
browser window that prompts you to log in to your Google account.
3. Log in to your Google account, and accept the OAuth2 prompt asking
you whether you want to allow Tableau Desktop to have access to your
BigQuery data. After you accept, your OAuth2 refresh token will be
cached, and you won't have to log in again unless you reinstall or revoke
the token. Tableau does not ever see your login credentials.
Figure 13.4
