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.
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.
You cannot use
LAG or any other analytic function for
value_expr. That is, you cannot nest analytic functions, but you can use other built-in function expressions for
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'; LAST_NAME HIRE_DATE SALARY PREV_SAL ------------------------- --------- ---------- ---------- Khoo 18-MAY-95 3100 0 Tobias 24-JUL-97 2800 3100 Baida 24-DEC-97 2900 2800 Himuro 15-NOV-98 2600 2900 Colmenares 10-AUG-99 2500 2600