oracle分析函式系列之LAG和LEAD:取出同一欄位的前N行的資料和後N行的值
阿新 • • 發佈：2019-02-04
Lag和Lead函式可以在一次查詢中取出同一欄位的前N行的資料和後N行的值。這種操作可以使用對相同表的表連線來實現，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函式為Lag(exp,N,defval)，defval是當該函式無值可用的情況下返回的值。Lead函式的用法類似。
Lead和Lag函式也可以使用分組，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
該函式也可以用於縱向錶轉橫向表、解釋示例：
SQL> select * from test_value;
MONS JJR CJL CJJE
---------- ---------- ---------- ----------
200801 LZF 250 1999
200802 LZF 200 2000
200803 LZF 300 1000
200804 LZF 23 189
200805 LZF 356 456
200806 LZF 100 200
200807 LZF 600 700
200808 LZF 23 123
200809 LZF 400 500
9 rows selected
SQL>
SQL> select rownum 序號,Mons,cjl cjl_01,
2 lead(cjl,1) over (order by mons desc) cjl_02,
3 lead(cjl,2) over (order by mons desc) cjl_03,
4 lead(cjl,3) over (order by mons desc) cjl_04,
5 lead(cjl,4) over (order by mons desc) cjl_05,
6 lead(cjl,5) over (order by mons desc) cjl_06,
7 lead(cjl,6) over (order by mons desc) cjl_07,
8 lead(cjl,7) over (order by mons desc) cjl_08,
9 lead(cjl,8) over (order by mons desc) cjl_09
10 from test_value 序號 MONS CJL_01 CJL_02 CJL_03 CJL_04 CJL_05 CJL_06 CJL_07 CJL_08 CJL_09
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
9 200809 400 23 600 100 356 23 300 200 250
8 200808 23 600 100 356 23 300 200 250
7 200807 600 100 356 23 300 200 250
6 200806 100 356 23 300 200 250
5 200805 356 23 300 200 250
4 200804 23 300 200 250
3 200803 300 200 250
2 200802 200 250
1 200801 250
該函式也可以用於縱向錶轉橫向表、解釋示例：
SQL> select * from test_value;
MONS JJR CJL CJJE
---------- ---------- ---------- ----------
200801 LZF 250 1999
200802 LZF 200 2000
200803 LZF 300 1000
200804 LZF 23 189
200805 LZF 356 456
200806 LZF 100 200
200807 LZF 600 700
200808 LZF 23 123
200809 LZF 400 500
9 rows selected
SQL>
SQL> select rownum 序號,Mons,cjl cjl_01,
2 lead(cjl,1) over (order by mons desc) cjl_02,
3 lead(cjl,2) over (order by mons desc) cjl_03,
4 lead(cjl,3) over (order by mons desc) cjl_04,
5 lead(cjl,4) over (order by mons desc) cjl_05,
6 lead(cjl,5) over (order by mons desc) cjl_06,
7 lead(cjl,6) over (order by mons desc) cjl_07,
8 lead(cjl,7) over (order by mons desc) cjl_08,
9 lead(cjl,8) over (order by mons desc) cjl_09
10 from test_value 序號 MONS CJL_01 CJL_02 CJL_03 CJL_04 CJL_05 CJL_06 CJL_07 CJL_08 CJL_09
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
9 200809 400 23 600 100 356 23 300 200 250
8 200808 23 600 100 356 23 300 200 250
7 200807 600 100 356 23 300 200 250
6 200806 100 356 23 300 200 250
5 200805 356 23 300 200 250
4 200804 23 300 200 250
3 200803 300 200 250
2 200802 200 250
1 200801 250