I like how the article teaches by explicit example. Very helpful when it comes to data.
The "lag" and "lead" SQL functions are particularly useful when analysing sequences of timestamped events (GPS fixes, task completions etc). They allow you to easily return the delta of a value (time/distance) between the current and previous row, which is really useful if you want to compare expected vs actual on those deltas.
The "lag" and "lead" SQL functions are particularly useful when analysing sequences of timestamped events (GPS fixes, task completions etc). They allow you to easily return the delta of a value (time/distance) between the current and previous row, which is really useful if you want to compare expected vs actual on those deltas.