lag, lead

Returns a value from a row before or after the current row in the window.

Syntax

lag( <expr> [, offset => <offset> ] [, default => <default_value> ] )
lead( <expr> [, offset => <offset> ] [, default => <default_value> ] )

Arguments

offset is an optional non-negative integer. The default is 1.

default is returned when the requested row is outside the window. The default is NULL.

Returns

Returns the same type as <expr>.

Examples

VALUES ('a'), ('b'), ('c')
WINDOW lag($0), lead($0);