Window Functions

SQL window function expressions.

WindowFunction

The WindowFunction class represents a window function. It includes a non-null window property indicating a window expression. Users should not need to instantiate WindowFunction instances directly, but instead should use window function methods such as row_number(), lag(), etc.

basis

WindowFunction.basis

The basis property indicates an underlying table column that can serve as a selection target for this window operation.

label

WindowFunction.label

The label property provides a descriptive text label.

over

WindowFunction.over(name)

Provide the name of a window definition for this function and returns a new WindowFunction instance. The window should be defined separately in an issued query, for example using the Query.window method.

partitionby

WindowFunction.partitionby(...expressions)

Provide one or more expressions by which to partition this window function and returns a new WindowFunction instance.

orderby

WindowFunction.orderby(...expressions)

Provide one or more expressions by which to sort this window function and returns a new WindowFunction instance.

rows

WindowFunction.rows(expression)

Provide a window "rows" frame specification as an array or array-valued expression and returns a new WindowFunction instance. A "rows" window frame is insensitive to peer rows (those that are tied according to the orderby criteria). The frame expression should evaluate to a two-element array indicating the number of preceding or following rows. A zero value (0) indicates the current row. A non-finite value (including null and undefined) indicates either unbounded preceding row (for the first array entry) or unbounded following rows (for the second array entry).

range

WindowFunction.range(expression)

Provide a window "range" frame specification as an array or array-valued expression and returns a new WindowFunction instance. A "range" window grows to include peer rows (those that are tied according to the orderby criteria). The frame expression should evaluate to a two-element array indicating the number of preceding or following rows. A zero value (0) indicates the current row. A non-finite value (including null and undefined) indicates either unbounded preceding row (for the first array entry) or unbounded following rows (for the second array entry).

row_number

row_number()

Create a window function that returns the number of the current row within the partition, counting from 1.

rank

rank()

Create a window function that returns the rank of the current row with gaps. This is the same as the row_number of its first peer.

dense_rank

dense_rank()

Create a window function that returns the rank of the current row without gaps, The function counts peer groups.

percent_rank

percent_rank()

Create a window function that returns the relative rank of the current row. Equal to (rank() - 1) / (total partition rows - 1).

cume_dist

cume_dist()

Create a window function that returns the cumulative distribution. (number of preceding or peer partition rows) / total partition rows.

ntile

ntile(num_buckets)

Create a window function that r an integer ranging from 1 to num_buckets, dividing the partition as equally as possible.

lag

lag(expression, offset, default)

Create a window function that returns the expression evaluated at the row that is offset rows before the current row within the partition. If there is no such row, instead return default (which must be of the same type as the expression). Both offset and default are evaluated with respect to the current row. If omitted, offset defaults to 1 and default to null.

lead

lead(expression, offset, default)

Create a window function that returns the expression evaluated at the row that is offset rows after the current row within the partition. If there is no such row, instead return default (which must be of the same type as the expression). Both offset and default are evaluated with respect to the current row. If omitted, offset defaults to 1 and default to null.

first_value

first_value(expression)

Create a window function that returns the expression evaluated at the row that is the first row of the window frame.

last_value

last_value(expression)

Create a window function that returns the expression evaluated at the row that is the last row of the window frame.

nth_value

nth_value(expression, nth)

Create a window function that returns the expression evaluated at the nth row of the window frame (counting from 1), or null if no such row.