新建两个表：

create table guotest1

(

sName varchar2(10),

Gender varchar2(10)

)

create table guotest2

(

sName varchar2(10),

Gender varchar2(10)

)

插入数据：

insert into guotest1 values('a', 'm');

insert into guotest1 values('b', 'm');

insert into guotest1 values('c', 'f');

insert into guotest1 values('d', 'f');

insert into guotest2 values('e', 'm');

insert into guotest2 values('f', 'm');

insert into guotest2 values('g', 'f');

insert into guotest2 values('h', 'f');

1 minus返回的是两个查询结果表的差集

例如：select * from guotest1 where rownum <= 4 minus select * from guotest1 where rownum <= 2

返回结果：

"SNAME","GENDER"

"c","f"

"d","f"

2 minus返回的记录总是来自于左边的表

例如：select * from guotest1 minus select * from guotest2

返回结果：

"SNAME","GENDER"

"a","m"

"b","m"

"c","f"

"d","f"

像是说：如果左边的表中的某个记录存在于右边的表中，则该记录不会返回

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