FYI: the FILTER expression is actually a port of the select expression. When you use FILTER, it’s just another way of writing SELECT() - when AppSheet is computing the formula, the FILTER() syntax is transposed into a SELECT. Just fyi.
Also another note to @Andrew_Hock:
In your post you put a sample SELECT():
While AppSheet does not require that all column names be unique, there are times when it could (perhaps it should enforce them, but that’s a discussion for another time), I have seen problems with some formulas not working solved by making column names different among tables.
If I had an invoice table, with Invoice_Details, Invoice_Notes, and other child tables, I wouldn’t call the reference column in each of the child tables “Invoice_Link” or “Invoice_ID”; instead I would individualize each of them (Invoice_Notes_Invoice_Link, Invoice_Details_Invoice_Link, etc.).
AppSheet has no limit to the length of a column name (that I’ve found), so you can get really detailed with the column names. Not only will this help you to be able to read your formulas and understand exactly what’s happening (without needing to know where it lives, context it’s used, etc.), but also any queries run on the back end will pan out correctly.