Oracle minus use

Create a new two table:

CREATE TABLE Guotest1

(

Sname VARCHAR2 (10),

Gender VARCHAR2 (10)

)

CREATE TABLE Guotest2

(

Sname VARCHAR2 (10),

Gender VARCHAR2 (10)

)

Insert data:

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 returns the difference set of two query result tables

For example: SELECT * from Guotest1 where rownum <= 4 minus select * from Guotest1 where rownum <= 2

return Result:

"Sname", "GENDER"

"C", "F"

"D", "F"

2 minus returned records always come from the table on the left

For example: SELECT * from Guotest1 minus select * from Guotest2

return Result:

"Sname", "GENDER"

"A", "M"

"B", "M"

"C", "F"

"D", "F"

This is like saying: If a record in the left table exists in the table on the right, the record does not return