sourceClause
The source clause introduces one or more aliased query sources. The from keyword is optional. Each source is an aliased expression or retrieve that can be referenced in subsequent clauses.
Examples
Single retrieve source
from [Encounter: "Inpatient Encounter"] E
Multiple sources (cross join)
from [Condition] C, [MedicationRequest] M
Source without 'from' keyword
[Condition] C where C.clinicalStatus ~ "Active"
EBNF
sourceClause
: 'from'? aliasedQuerySource (',' aliasedQuerySource)*
;