[dragonwriter]

> It can't work them out because you compose the query in a third party scripting language.

The restrictions on what language features you can use in lambdas inside queries exist because the query isn't executed on the client, the query in the client language is parsed into a client-language-independent query description which is shipped back to the server and executed on the server. So all the information about the query is available to the server (how much it actually uses for optimization, I don't know, but the query is not opaque to the server; what is composed in the scripting language has the same relation to what the server sees as when you use an SQL abstraction layer that builds SQL and sends it back to the server with an SQL DB.)