A表两个KEY,B表一个KEY,两个表结合显示,B表就会有许多数据重复,想把重复的数据设为空,怎么写SQL好啊
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------解决方案--------------------
SQL> select A.akey1,
2 A.akey2,
3 A.afield1,
4 A.afield2,
5 B.bkey1,
6 decode(max(A.akey2) over(partition by A.akey1,B.bkey1),A.akey2,B.bfield1,null) as bfield1,
7 decode(max(A.akey2) over(partition by A.akey1,B.bkey1),A.akey2,B.bfield2,null) as bfield2
8 from (select 2 as akey1,1 as akey2, 'aaa ' as afield1, '111a ' as afield2 from dual
9 union all
10 select 1 as akey1,2 as akey2, 'bbb ' as afield1, '111b ' as afield2 from dual
11 union all
12 select 3 as akey1,3 as akey2, 'ccc ' as afield1, '111c ' as afield2 from dual
13 union all
14 select 2 as akey1,4 as akey2, 'ddd ' as afield1, '111d ' as afield2 from dual
15 union all
16 select 3 as akey1,5 as akey2, 'eee ' as afield1, '111e ' as afield2 from dual
17 )A,
18 (
19 select 1 as bkey1, 'a111 ' as bfield1, 'ab111 ' as bfield2 from dual
20 union all
21 select 2 as bkey1, 'b111 ' as bfield1, 'bb111 ' as bfield2 from dual
22 union all
23 select 3 as bkey1, 'c111 ' as bfield1, 'cb111 ' as bfield2 from dual
24 )B
25 where A.akey1 = B.bkey1;

AKEY1 AKEY2 AFIELD1 AFIELD2 BKEY1 BFIELD1 BFIELD2
---------- ---------- ------- ------- ---------- ------- -------
1 2 bbb 111b 1 a111 ab111
2 1 aaa 111a 2
2 4 ddd 111d 2 b111 bb111
3 3 ccc 111c 3
3 5 eee 111e 3 c111 cb111