See Also:"Analytic Functions" for information on syntax, semantics, and restrictions, including valid forms of
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.
For the optional
offset argument, specify an integer that is greater than zero. 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.
NULLS determines whether null values of
value_expr are included in or eliminated from the calculation. The default is
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
The following example provides, for each purchasing clerk in the
employees table, the salary of the employee hired just before:
SELECT hire_date, last_name, salary, LAG(salary, 1, 0 ) OVER (ORDER BY hire_date) AS prev_sal FROM employees WHERE job_id = 'PU_CLERK' ORDER BY hire_date; HIRE_DATE LAST_NAME SALARY PREV_SAL --------- ------------------------- ---------- ---------- 18-MAY-03 Khoo 3100 0 24-JUL-05 Tobias 2800 3100 24-DEC-05 Baida 2900 2800 15-NOV-06 Himuro 2600 2900 10-AUG-07 Colmenares 2500 2600