Within Direct Discovery, there are three types of data fields: DIMENSION, MEASURE, and DETAIL. The types are set on data fields when the Direct Discovery selection is made using the Direct Query statement in the load script.
Fore more information, see Direct Query.
All Direct Discovery fields can be used in combination with in-memory fields. Typically, fields with discrete values that will be used as dimensions should be loaded with the DIMENSION keyword, whereas numeric data that will be used in aggregations only should be marked as MEASURE fields.
The following table summarizes the characteristics and usage of the Direct Discovery field types:
|Used in chart expressions?
DIMENSION fields are loaded in memory and can be used to create associations between in-memory data and the data in Direct Discovery fields. Direct DiscoveryDIMENSION fields are also used to define dimension values in charts.
MEASURE fields, on the other hand, are recognized on a "meta level." MEASURE fields are not loaded in memory (they do not appear in the data model viewer).The purpose is to allow aggregations of the data in MEASURE fields to take place in the database rather than in memory. Nevertheless, MEASURE fields can be used in expressions without altering the expression syntax. As a result, the use of Direct Discovery fields from the database is transparent to the end user.
The following aggregation functions can be used with MEASURE fields:
- Sum - chart function
- Avg - chart function
- Count - chart function
- Min - chart function
- Max - chart function
DETAIL fields provide information or details that you may want to display but not use in chart expressions. Fields designated as DETAIL commonly contain data that cannot be aggregated in any meaningful way, like comments.
Any field can be designated as a DETAIL field.