Oracle plsql lead function

ORACLE/PLSQL: LEAD FUNCTION This Oracle tutorial explains how to use the Oracle/PLSQL LEAD function with syntax and examples.

DESCRIPTION The Oracle/PLSQL LEAD function is an analytic function that lets you query more than one row in a table at a time without having to join the table to itself. It returns values from the next row in the table. To return a value from a previous row, try using the LAG function.

SYNTAX The syntax for the Oracle/PLSQL LEAD function is: LEAD ( expression [, offset [, default] ] ) over ( [ query_partition_clause ] order_by_clause )

Parameters or Arguments expression is an expression that can contain other built­in functions, but can notcontain any analytic functions. offset is optional. It is the physical offset from the current row in the table. If this parameter is omitted, the default is 1. default is optional. It is the value that is returned if the offset goes out of the bounds of the table. If this parameter is omitted, the default is null.

APPLIES TO The LEAD function can be used in the following versions of Oracle/PLSQL: Oracle 12c, Oracle 11g, Oracle 10g, Oracle 9i, Oracle 8i

EXAMPLE The LEAD function can be used in Oracle/PLSQL. Let's look at an example. If we had an orders table that contained the following data:

ORDER_DATE PRODUCT_ID QTY 25/09/2007

1000

20

26/09/2007

2000

15

27/09/2007

1000

8

28/09/2007

2000

12

29/09/2007

2000

2

30/09/2007

1000

4

And we ran the following SQL statement: select product_id, order_date, LEAD (order_date,1) over (ORDER BY order_date) AS next_order_date from orders;

It would return the following result:

PRODUCT_ID ORDER_DATE NEXT_ORDER_DATE 1000

25/09/2007

26/09/2007

2000

26/09/2007

27/09/2007

1000

27/09/2007

28/09/2007

2000

28/09/2007

29/09/2007

2000

29/09/2007

30/09/2007

1000

30/09/2007

<NULL>

Since we used an offset of 1, the query returns the next order_date.

If we had used an offset of 2 instead, it would have returned the order_date from 2 orders later. If we had used an offset of 3, it would have returned the order_date from 3 orders later....and so on.

If we wanted only the orders for a given product_id, we could run the following SQL statement:

select product_id, order_date, LEAD (order_date,1) over (ORDER BY order_date) AS next_order_date from orders where product_id = 2000;

It would return the following result:

PRODUCT_ID ORDER_DATE NEXT_ORDER_DATE 2000

26/09/2007

28/09/2007

2000

28/09/2007

29/09/2007

2000

29/09/2007

<NULL>

In this example, it returned the next order_date for product_id = 2000 and ignored all other orders.