Skip Headers
Oracle® Database SQL Language Reference
11g Release 2 (11.2)

Part Number E17118-03
Go to Documentation Home
Home
Go to Book List
Book List
Go to Table of Contents
Contents
Go to Index
Index
Go to Master Index
Master Index
Go to Feedback page
Contact Us

Go to previous page
Previous
Go to next page
Next
View PDF

LAG

Syntax

Description of lag.gif follows
Description of the illustration lag.gif

See Also:

"Analytic Functions" for information on syntax, semantics, and restrictions, including valid forms of value_expr

Purpose

LAG is an analytic function. It provides access to more than one row of a table at the same time without a self join. Given a series of rows returned from a query and a position of the cursor, LAG provides access to a row at a given physical offset prior to that position.

If you do not specify offset, then its default is 1. The optional default value is returned if the offset goes beyond the scope of the window. If you do not specify default, then its default is null.

{RESPECT | IGNORE} NULLS determines whether null values of value_expr are included in or eliminated from the calculation. The default is RESPECT NULLS.

You cannot nest analytic functions by using LAG or any other analytic function for value_expr. However, you can use other built-in function expressions for value_expr.

See Also:

"About SQL Expressions" for information on valid forms of expr and LEAD

Examples

The following example provides, for each salesperson in the employees table, the salary of the employee hired just before:

SELECT last_name, hire_date, salary,
       LAG(salary, 1, 0) OVER (ORDER BY hire_date) AS prev_sal
  FROM employees
  WHERE job_id = 'PU_CLERK'
  ORDER BY last_name, hire_date, salary;
   
LAST_NAME                 HIRE_DATE     SALARY   PREV_SAL
------------------------- --------- ---------- ----------
Baida                     24-DEC-05       2900       2800
Colmenares                10-AUG-07       2500       2600
Himuro                    15-NOV-06       2600       2900
Khoo                      18-MAY-03       3100          0
Tobias                    24-JUL-05       2800       3100