One output column of a Group or a window: a function of a column, under a
name. The function is kept as saved, so an unknown or empty one is held and
reported, never dropped (PLAN §11.5, Q4). column is undefined for a
function that takes none (Count rows, the rank functions) and '' until
picked; name is '' until given. offset (Lag, Lead), buckets
(NTile), percentile (Percentile) and separator (Join Text) are their
functions' settings (PLAN §11.9, §11.28), kept as given for validation to
judge, and undefined on every other function.
One output column of a Group or a window: a function of a column, under a name. The function is kept as saved, so an unknown or empty one is held and reported, never dropped (PLAN §11.5, Q4).
columnisundefinedfor a function that takes none (Count rows, the rank functions) and''until picked;nameis''until given.offset(Lag, Lead),buckets(NTile),percentile(Percentile) andseparator(Join Text) are their functions' settings (PLAN §11.9, §11.28), kept as given for validation to judge, andundefinedon every other function.