lag, lead
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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);