1，UNION对数据进行排序，并压缩重复数据；
SQL> select * from test3;
ID LNAME FNAME
---------- -------------------- --------------------
14 kong unkown
15 kongkong unkown
55 kong3 unknow
SQL> select * from test3
2 union
3 select * from test3;
ID LNAME FNAME
---------- -------------------- --------------------
14 kong unkown
15 kongkong unkown
55 kong3 unknow
SQL> select * from test3
2 union all
3 select * from test3;
ID LNAME FNAME
---------- -------------------- --------------------
14 kong unkown
15 kongkong unkown
55 kong3 unknow
14 kong unkown
15 kongkong unkown
55 kong3 unknow
已选择6行。
2，交集INTERSECT;
SQL> select id,lname from test3 where id>14;
ID LNAME
---------- --------------------
15 kongkong
55 kong3
SQL> select id,lname from test3 where lname like '%3%';
ID LNAME
---------- --------------------
55 kong3
SQL> select id,lname from test3 where id>14
2 intersect
3 select id,lname from test3 where lname like '%3%';
ID LNAME
---------- --------------------
55 kong3
3，差集：MINUS;
SQL> run
1 select id,lname from test3 where id>14
2 minus
3* select id,lname from test3 where lname like '%3%'
ID LNAME
---------- --------------------
15 kongkong
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