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Amazon Redshift
Database Developer Guide (API Version 2012-12-01)

LAG Window Function Examples

The following example shows the quantity of tickets sold to the buyer with a buyer ID of 3 and the time that buyer 3 bought the tickets. To compare each sale with the previous sale for buyer 3, the query returns the previous quantity sold for each sale. Since there is no purchase before 1/16/2008, the first previous quantity sold value is null:

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select buyerid, saletime, qtysold, lag(qtysold,1) over (order by buyerid, saletime) as prev_qtysold from sales where buyerid = 3 order by buyerid, saletime; buyerid | saletime | qtysold | prev_qtysold ---------+---------------------+---------+-------------- 3 | 2008-01-16 01:06:09 | 1 | 3 | 2008-01-28 02:10:01 | 1 | 1 3 | 2008-03-12 10:39:53 | 1 | 1 3 | 2008-03-13 02:56:07 | 1 | 1 3 | 2008-03-29 08:21:39 | 2 | 1 3 | 2008-04-27 02:39:01 | 1 | 2 3 | 2008-08-16 07:04:37 | 2 | 1 3 | 2008-08-22 11:45:26 | 2 | 2 3 | 2008-09-12 09:11:25 | 1 | 2 3 | 2008-10-01 06:22:37 | 1 | 1 3 | 2008-10-20 01:55:51 | 2 | 1 3 | 2008-10-28 01:30:40 | 1 | 2 (12 rows)