That's alot of work. I work in shipping/logistics connecting clients to carriers for rating, shipping, and labeling purposes. The custom needs of the client are what really makes the queries begin to balloon and become convoluted... or because they might use the same database that another client uses (or WMS if you prefer) while using different fields or storing different data in the same fields. Then they expect that everyone is doing things the same way as they are.

Creating SQL queries can be fun to develop and super-challenging to get right, especially if you're joining like 16 tables together.