A query against a semantic model that returns a table, comparable to a T-SQL SELECT. It is written with EVALUATE, optionally preceded by DEFINE for query-only measures and variables and followed by ORDER BY, and it doesn't alter the model.
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Each book explains DAX query in context, with comparison tables and the common traps.
Terms in this definition
- Semantic model
Sometimes called an OLAP model, this Power BI and Fabric layer defines the measures, hierarchies, tables and relationships that reports and dashboards query; star schema design is the usual pattern.
- Event
Table in Log Analytics where entries from Windows event logs are kept.
- T-SQL
The dialect of SQL that Microsoft uses for Azure SQL and SQL Server. Azure Monitor logs are queried with KQL instead.
- SELECT
A DML command in SQL used to retrieve rows from one table or several.
- EVALUATE
Keyword that every DAX query must contain; whatever table expression follows it becomes the query's output. Clauses such as DEFINE, ORDER BY and START AT may be added if needed.
- DEFINE
An optional keyword at the start of a DAX query, placed before the first EVALUATE, for declaring things such as measures and variables that exist only for that query. A measure declared this way replaces a model measure with the same name just while the query runs.
- ORDER BY
Sorts what a SQL query returns on one or more columns. Leave it out and rows arrive in no guaranteed sequence.
Related terms
- Formula engine
Plans how a DAX query will be answered inside a semantic model, then asks the storage engine, VertiPaq for Import and Direct Lake, to fetch data and do the first aggregations.
- Performance analyzer
Times every visual on a report page as it loads, splitting the result into DAX query and render time; you can copy each visual's query or open it in DAX query view. It is available in Power BI Desktop and while editing reports in the service.