expression
Parameters
value
The math expression to perform on the returned data, if this object is performing a math expression. This expression can use the `Id`
of the other metrics to refer to those metrics, and can also use the `Id`
of other expressions to use the result of those expressions. Conditional: Within each `TargetTrackingMetricDataQuery`
object, you must specify either `Expression`
or `MetricStat`
, but not both.