Although the transformation language is based on standard SQL, there are difference between the two languages. For example, SQL supports the keywords ALL and DISTINCT for aggregate functions, but the transformation language does not. On the other hand, the transformation language supports an optional filter condition for aggregate functions, while SQL does not.
You can create an expression that is as simple as a port (such as ORDERS), a pre-defined workflow variable (such as $Start.Status), or a numeric literal (such as 10). You can also write complex expressions that include functions nested within functions, or combine different columns using the transformation language operators.