first(expression: storable, [order_by(...)]?) -> expression

Return the first value of one column across an ordered group.

If no ordering is specified, the default ordering is that of the invoking verb, which is generally the 'valid_from' timestamp, ascending. In this case, the first value is the earliest.

Domain

This is an aggregate function (aggregates rows over a group in aggregate verbs).

This is a window function (calculates over a group of multiple input rows using windowing).

Categories

• Aggregate
• Window

Examples

make_col first_customer:window(first(customer_id), group_by(category))

Find out the customer that appears first within each category.

statsby first_customer:first(customer_id), group_by(category)

Find out the customer that appears first within each category.

statsby first_customer:first(customer_id, order_by(login_time)), group_by(category)

Find out the customer that logged in first within each category.