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Returns the value of the input expression at the given offset before the current row within the requested window.

For more information on usage, please refer to Window Functions.


LAG ( <expression> [, <offset> [, <default> ]] )
    OVER ( [ PARTITION BY <partition_by> ] ORDER BY <order_by> [ { ASC | DESC } ] )


Parameter Description Supported input types
<value> Any valid expression that will be returned based on the <offset>. Any
<partition_by> The expression used for the PARTITION BY clause. Any
<offset> The number of rows backward from the current row from which to obtain a value. A negative number will act as LEAD() INTEGER
<default> The expression to return when the offset goes out of the bounds of the window. Must be a literal INTEGER. The default is NULL. INTEGER
<order_by> An expression used for the order by clause. Any


In the example below, the LAG function is being used to find the players in each level who ranked above and below a certain player. In some cases, if the player has no one ranked above or below them, the LAG function returns NULL.

	LAG(nickname, 1) OVER (PARTITION BY level ORDER BY nickname ) AS rank_above,
	LAG(first_name, -1) OVER (PARTITION BY level ORDER BY first_name ) AS rank below


nickname level rank_above rank_below
kennethpark 9 NULL rileyjon
rileyjon 9 kennethpark sabrina21
sabrina21 9 rileyjon ymatthews
ymatthews 9 sabrina21 NULL