LAG:
Using this function we can fetch the nth row before (Lag) the Current row without using self-join.
It is useful when we need to compare the current row values with values in a previous row.
Syntax:
LAG (scalar_expression [,offset] [,default])
OVER ( [ partition_by_clause ] order_by_clause )
EXAMPLE:
Create an Employee table and insert some records to it.
CREATE TABLE Employee (EmpID int, HikeDate date, Salary money)
GO
INSERT INTO employee values (1, '2009-04-01 00:00:00.000',10000),
(1, '2010-04-01 00:00:00.000',17000),
(1, '2011-04-01 00:00:00.000',23000)
GO
SELECT EmpID, HikeDate, Salary
FROM Employee
ORDER BY HikeDate
Output:
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Now my requirement is to show what the previous Salary before current hike was?
Solution Using Lag function:
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LEAD:
Using this function we can fetch the nth row after (LEAD) the current row without using self-join.
It is useful when we need to compare the current row values with values in a following row.
Syntax:
LEAD (scalar_expression [,offset] [,default])
OVER ( [ partition_by_clause ] order_by_clause )
Example:
My requirement is to show what my following year salary is?
Solution using Lead function:
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Note: Default offset value is 1. We can specify offset value by a column or a sub query, or other expression that evaluates to a positive integer. Negative value or analytical function can’t be used as offset value.
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