Island Aggregates: Length, Start, End

Concepts covered: sqlLagLead

The other common variant is conditional islands. The runs are not defined by adjacency at all; they are defined by a status or attribute being constant for a stretch of rows. 'Find contiguous periods where a subscription was active.' 'Find stretches where a server was healthy.' 'Find runs of days the stock closed above its 50-day moving average.' These are gaps and islands where 'consecutive' means 'sharing the same value' rather than 'adjacent in the sequence.' The LAG form handles this case cleanly with one change to the boundary CASE. The status-change variant What changed in the boundary CASE The boundary condition is no longer about a time gap; it is about a value change. is_new_run is 1 when the predecessor's status is different from the current row's status (or when there is no pred

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