如何使用oracle的LAG和LEAD 等統計函數

Lag和Lead函數可以在一次查詢中取出同一字段的前N行的數據和后N行的值。這種操作可以使用對相同表的表連接來實現，不過使用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)

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

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

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

YEAR REGION????? PROFIT NEXT_YEAR_EXP

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

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

2003 West??????????? 88?????????? 101

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

2003 Central??????? 100?????????? 102

2003 East?????????? 102??????????? 77

2004 West??????????? 77?????????? 103

2004 East?????????? 103??????????? 89

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

Lag函數為Lag(exp,N,defval)，defval是當該函數無值可用的情況下返回的值。Lead函數的用法類似。

Lead和Lag函數也可以使用分組，以下是使用region分組的例子：

SQL> select year,region,profit ,

2 lag (profit,1,0) over (PARTITION BY region order by year)

3?????? as last_year_exp from test;

YEAR REGION????? PROFIT LAST_YEAR_EXP

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

2003 Central??????? 101???????????? 0

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

2003 East?????????? 102???????????? 0

2004 East?????????? 103?????????? 102

2003 West??????????? 88???????????? 0

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

2004 West??????????? 77??????????? 88

2004 West??????????? 89??????????? 77

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