letClause
Introduces one or more named sub-expressions within a query. Let-bound names may be used in subsequent clauses such as where, return, and aggregate, avoiding repeated evaluation of the same expression.
Examples
Single let binding
from [Encounter] E let period: E.period where period during "Measurement Period"
Multiple let bindings
from [Observation] O
let value: O.value as Quantity,
unit: O.value.unit
return Tuple { value: value, unit: unit }EBNF
letClause
: 'let' letClauseItem (',' letClauseItem)*
;