expressions in the output namespace (having,group_by)

[mtoy-googly-moogly]

As of this writing, things are a little broken.

• having: and top: by expressions can only reference fields in the source namespace
• order_by: can only reference fields in the query result namespace

Perhaps we should make "reference to the result namepace" something which is explicit. This raises the question, "What are the contexts in which it would be reasonable to access both the query (output) namespace and the source (input) namespace?"

Sometimes when referencing a namespace, you really can only reference aggregates, or non-aggregates from that namespace and so maybe as we formalize this, we include this "filtered namespace" notion ...

This table is not correct, but is a placeholder for a more correct table.

Reference	Query	Source
group_by: definitions	None	Dimensions
aggregate: definitions	None	Full
project: definitions	None	Dimensions
where: expressions	None	Dimensions
having: expressions	Full	Full
order_by: expressions	Full	Full
top: N by name	Full	Full

What is the syntax for a reference to a field in the result.

1. A magic identifier, like RESULT.measureInQuery / measureInSource
   • I worry about losing a keyword here, I’d prefer not to do this. What is great about this is that the word RESULT itself shows what the syntax means. This is something like self. and may also suggest a way to get at the namespace of a the Malloy gesture which replaces window functions.
2. Dot with no identifier .measureInQuery / measureInSource
   • This could work. Concerns are, does this screw the expression grammar, and how noticeable will it be when reading code.
3. A sigil ($, &, @, :>, etc), like $measureInQuery / measureInSource
   • This is more punctuation salad, which I have bias against. I’d prefer something about the syntax of the reference to suggest why the reference is special instead of just a magic character. EXCEPT what if the sigil was ?measureInQuery … does the question mark there suggest the association with the query result ?
4. A container, { measureInQuery } / measureInSource
   • Every identifier inside the {} is evaluated in the query/output namespace. This is less obvious than RESULT. but using {} to show a new namespace with different properties than the namespace before the {} is a thing in Malloy.
5. Use the query sigil somehow: order_by: ->measureInQuery / srcMeasure
   • I am not sure how this would read, I can imagine this making sense, I can also imagine it being confusing.