Apr 28, 2012

Lead and Lag Functions in SQL Server

SQL Server 2012 introduced new analytical function LEAD() and LAG().

These functions accesses data from nth next row and nth previous row in the same result set without the use of a self-join
  • LEAD():  Used to access data from nth next row in the same result set without the use of a self-join.
  • LAG(): Used to access data from nth previous row in the same result set without the use of a self-join
Syntax
LEAD (scalar_expression [,offset] [,default])
    OVER ( [ partition_by_clause ] order_by_clause )

LAG (scalar_expression [,offset] [,default])
    OVER ( [ partition_by_clause ] order_by_clause )

Parameters
  • scalar_expression: column name for which value to be accessed
  • offset: nth previous (for lag) or next (for lead) row  to access of the column
  • default: default value to display if nth row not exists

Example - 1
DECLARE @Test_table TABLE(
    Year INT, Sale INT
)

INSERT INTO @Test_table VALUES
('2008',5000000), ('2009',5500000), ('2010',5250000), ('2011',6025000), ('2012',6200000)

SELECT    Year, Sale
        , LEAD(Sale) OVER (ORDER BY Year) AS [Next Year Sale]
        , LAG(Sale) OVER (ORDER BY Year) AS [Prev Year Sale]
        , LEAD(Sale, 2) OVER (ORDER BY Year) AS [2nd Next Year Sale]
        , LAG(Sale, 2) OVER (ORDER BY Year) AS [2nd Prev Year Sale]
        , LEAD(Sale, 2, 0) OVER (ORDER BY Year) AS [2nd Next Year Sale]
        , LAG(Sale, 2, 0) OVER (ORDER BY Year) AS [2nd Prev Year Sale]
FROM    @Test_table
RESULT
Lead & Lag Output

Example - 2 (With Partition By)
DECLARE @Test_table TABLE(
    Year INT, Zone VARCHAR(10),  Sale INT
)

INSERT INTO @Test_table VALUES
 ('2009', 'East', 5500000), ('2010', 'East', 5250000), ('2011', 'East', 6025000), ('2012', 'East', 6200000)
,('2009', 'West', 5200000), ('2010', 'West', 5250000), ('2011', 'West', 5525000), ('2012', 'West', 5700000)
,('2009', 'North', 4700000), ('2010', 'North', 4800000),('2011', 'North', 5000000), ('2012', 'North', 5050000)
,('2009', 'South', 7200000), ('2010', 'South', 7500000), ('2011', 'South', 7800000), ('2012', 'South', 8000000)

SELECT    Year, Sale
        , LEAD(Sale) OVER (PARTITION BY Zone ORDER BY Year) AS [Next Year Sale]
        , LAG(Sale) OVER (PARTITION BY Zone ORDER BY Year) AS [Prev Year Sale]
        , LEAD(Sale, 2) OVER (PARTITION BY Zone ORDER BY Year) AS [2nd Next Year Sale]
        , LAG(Sale, 2) OVER (PARTITION BY Zone ORDER BY Year) AS [2nd Prev Year Sale]
        , LEAD(Sale, 2, 0) OVER (PARTITION BY Zone ORDER BY Year) AS [2nd Next Year Sale]
        , LAG(Sale, 2, 0) OVER (PARTITION BY Zone ORDER BY Year) AS [2nd Prev Year Sale]
FROM    @Test_table
RESULT
Lead & Lag Output

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