First Function in OBIEE
This function selects the first returned value of the expression argument. For example, the FIRST function can calculate the value of the first day of the year.
The FIRST function is limited to defining dimension-specific aggregation rules in a repository. You cannot use it in SQL statements.
The FIRST function operates at the most detailed level specified in your explicitly defined dimension. For example, if you have a time dimension defined with hierarchy levels day, month, and year, the FIRST function returns the first day in each level.
You should not use the FIRST function as the first dimension-specific aggregate rule. It might cause queries to bring back large numbers of rows for processing in the Oracle BI Server, causing poor performance.
When a measure is based on dimensions, and data is dense, the Oracle BI Server optimizes the SQL statements sent to the database to improve performance.
Note that you cannot nest PERIODROLLING, FIRST, and LAST functions.
expr is any expression that references at least one measure column.