11g之后的oracle版本。
一致的状况:存在性判断的话,不影响结果。
CREATE TABLE students (
ID NUMBER ,
NAME VARCHAR2(20)
)
CREATE TABLE lesson (
ID NUMBER ,
kc VARCHAR2(20)
)
TRUNCATE TABLE students
INSERT INTO students VALUES (1,'ws');
INSERT INTO students VALUES (2,'gw');
INSERT INTO students VALUES (4,'jr');
INSERT INTO lesson VALUES (1,'sx');
INSERT INTO lesson VALUES (2,NULL);
INSERT INTO lesson VALUES (3,NULL);
INSERT INTO lesson VALUES (NULL,NULL);
SELECT * FROM students;
SELECT * FROM lesson;
SELECT * FROM students s
WHERE NOT EXISTS (
SELECT 1 FROM lesson l WHERE s.id = l.id
)
SELECT * FROM students s WHERE s.id NOT IN
(
SELECT 1 FROM lesson WHERE 1=23
)
不一致的情况:
比对字段内的值的情况,如果有null会影响判断。
SELECT * FROM students s WHERE s.id NOT IN
(
SELECT id FROM lesson
)