Lag和Lead函数可以在一次查询中取出同一字段的前N行的数据和后N行的值。这种操作可以使用对相同表的表连接来实现，不过使用LAG和LEAD有更高的效率。以下是LAG和LEAD的例子：

SQL> select year,region,profit ,lag (profit,1) over (order by year)

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2?????? as last_year_exp from test;

?

YEAR REGION????? PROFIT LAST_YEAR_EXP

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

2003 West??????????? 88

2003 West??????????? 88??????????? 88

2003 Central??????? 101??????????? 88

2003 Central??????? 100?????????? 101

2003 East?????????? 102?????????? 100

2004 West??????????? 77?????????? 102

2004 East?????????? 103??????????? 77

2004 West??????????? 89?????????? 103

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SQL> select year,region,profit ,lead (profit,1) over (order by year)

?

2?????? as next_year_exp from test;