Learn about row context
Now that you've created calculated columns, you can learn how their formulas are evaluated.
The formula for a calculated column is evaluated for each table row. Furthermore, it's evaluated within row context, which means the current row. Consider the Due Fiscal Year calculated column definition:
Due Fiscal Year = "FY" & YEAR('Due Date'[Due Date]) + IF( MONTH('Due Date'[Due Date]) <= 6, 1 )
When the formula is evaluated for each row, the
'Due Date'[Due Date] column reference returns the column value for that row. You'll find that Microsoft Excel has the same concept for working with formulas in Excel tables.
However, row context doesn't extend beyond the table. If your formula needs to reference columns in other tables, you have two options:
- If the tables are related, directly or indirectly, you can use the
RELATEDTABLEDAX function. The
RELATEDfunction retrieves the value at the one-side of the relationship, while the
RELATEDTABLEretrieves values on the many-side. The
RELATEDTABLEfunction returns a table object.
- When the tables aren't related, you can use the
Generally, try to use the
RELATED function whenever possible. It will usually perform better than the
LOOKUPVALUE function due to the ways that relationship and column data is stored and indexed.
Now, add the following calculated column definition to the Sales table:
Discount Amount = ( Sales[Order Quantity] * RELATED('Product'[List Price]) ) - Sales[Sales Amount]
The calculated column definition adds the Discount Amount column to the Sales table. Power BI evaluates the calculated column formula for each row of the Sales table. The values for the Order Quantity and Sales Amount columns are retrieved within row context. However, because the List Price column belongs to the Product table, the
RELATED function is required to retrieve the list price value for the sale product.
Row context is used when calculated column formulas are evaluated. It's also used when a class of functions, known as iterator functions, are used. Iterator functions provide you with flexibility to create sophisticated summarizations. Iterator functions are described in a later module.