OBIEE - How to Set a Temp Query Logging Level?

You might want to diagnose performance or data issues by setting a temporary log level for a query. You can enable query logging for a select statement by adding a prefix clause in the Advanced SQL Clauses section of the Advanced tab in Oracle BI Presentation Services.
For example, for the select statement:
SELECT a, b, c from dim1, fact 1;
You can specify the logging level of 5 in the Prefix field as follows:

Set Variable LOGLEVEL=5;

For this query, the logging level of 5 is used regardless of the value of the underlying LOGLEVEL variable.