Working with a Data Extract

1. Extract Data

An extract is a copy of the data that brought into the Tableau data engine.

Use the Tableau data engine to run queries rather than send a query to the data source
- Reduce the time it takes for queries to run
Allow you to keep a copy of the data:
- Can be accessed offline
May include only a subset of the data

Data doesn’t update automatically
- Need to refresh the Extract
- A Live connection queries the data from the database and the data are updated every time you open your workbook
Your extracted data source may not include all the fields required for the views
- Because extracts may include only a subset of the data

From the Data Source page
On the worksheet

- [Data] Pane --> right-click the data source --> [Use Extract]

- Switch between a live or extracted data connection: check / uncheck [Use Extract]

From the data source page
On the worksheet

- [Data] Pane --> right-click the data source --> [Extract Data]

[Edit extracts from the Extract Data dialog box]

Hide unused fields
Unhide fields
- [Data] Pane --> right-click --> [Show Hidden Fields]
- Field to show --> right-click --> check [Unhide]

[Tableau Help] – Refresh Extracts (中：刷新数据提取 / 한: 추출 새로 고침)

Full extract refresh (default) [完全刷新]
- all of the rows are replaced with the data in the original data source
- [good] ensures that you have an exact copy of what is in the original data
- [bad] can sometimes take a long time and be expensive on the database
Incremental extract refresh [增量刷新]
- configure a refresh to add only the rows that are new since the previous time you extracted the data
- Note: If the data structure of the source data changes (for example, a new column is added), you will need to do a full extract refresh before you can start doing incremental refreshes again.