다음 행의 데이터를 가져오는 LEAD 함수

현재 위치의 정보를 보여주고 다음 목적지의 이름을 가져와야 하는데 뭔가 간단한 방법이 있지 않을까 해서 알아보니 오라클에 LEAD() 라는 함수가 존재하더군요.

LEAD() 함수 덕분에 간단하게 다음 로우에 있는 데이터를 가져 올 수 있게 되었네요.

반대로 이전 로우의 데이터를 가져 올 때는 LAG() 라는 함수를 같은 방식으로 사용하면 됩니다.

아래는 오라클 사이트에서의 LEAD() 함수에 대한 설명 원문입니다.

Syntax

Description of the illustration lead.gif

See Also:

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

Purpose

LEAD 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, LEAD provides access to a row at a given physical offset beyond 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 table. If you do not specify default, then its default value is null.

You cannot nest analytic functions by using LEAD 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 LAG

Examples

The following example provides, for each employee in the employees table, the hire date of the employee hired just after:

SELECT last_name, hire_date, 


   LEAD(hire_date, 1) OVER (ORDER BY hire_date) AS "NextHired" 


   FROM employees WHERE department_id = 30


   ORDER BY last_name, hire_date, "NextHired";




LAST_NAME                 HIRE_DATE NextHired


------------------------- --------- ---------


Baida                     24-DEC-97 15-NOV-98


Colmenares                10-AUG-99


Himuro                    15-NOV-98 10-AUG-99


Khoo                      18-MAY-95 24-JUL-97


Raphaely                  07-DEC-94 18-MAY-95


Tobias                    24-JUL-97 24-DEC-97

출처 : http://download.oracle.com/docs/cd/B28359_01/server.111/b28286/functions079.htm#i83834