Oracle第二课（学习中笔记）

What is a join?

1.Equijoin

2.Non-equijoin

3.Outer join

4. Self join

1、等值连接

SELECT A.ID,A.NAME,B.CNAME FROM TABLE1 A,TBALE2 B WHERE A.ID=B.CID;

建立多个表

1。学生表(JUL12_STUDENT_04)

CREATE TABLE JUL12_STUDENT_04(

SID NUMBER(4),

SNAME VARCHAR2(20),

CID NUMBER(4)

);

INSERT INTO JUL12_STUDENT_04 VALUES (101,'ZHANG',1);

INSERT INTO JUL12_STUDENT_04 VALUES (102,'SHELI',2);

INSERT INTO JUL12_STUDENT_04 VALUES (103,'GUOSHEN',1);

INSERT INTO JUL12_STUDENT_04 VALUES (104,'WEB',2);

INSERT INTO JUL12_STUDENT_04 VALUES (105,'LUEHUA',1);

INSERT INTO JUL12_STUDENT_04 VALUES (106,'HEJING',2);

INSERT INTO JUL12_STUDENT_04 VALUES (107,'WEN',1);

INSERT INTO JUL12_STUDENT_04 VALUES (108,'JIANG',2);

2。班级表(JUL12_CLASS_04)

CREATE TABLE JUL12_CLASS_04(

CID NUMBER(4),

CNAME VARCHAR2(20)

);

INSERT INTO JUL12_CLASS_04 VALUES (1,'SD0001');

INSERT INTO JUL12_CLASS_04 VALUES (2,'SD0002');

INSERT INTO JUL12_CLASS_04 VALUES (3,'SD0003');

3。课程表(JUL12_LESSION_04)

CREATE TABLE JUL12_LESSION_04(

LID NUMBER(4),

LNAME VARCHAR2(20)

);

INSERT INTO JUL12_LESSION_04 VALUES (100,'MATH');

INSERT INTO JUL12_LESSION_04 VALUES (101,'ENG');

INSERT INTO JUL12_LESSION_04 VALUES (102,'FHY');

4。学生课程表(JUL12_S_L_04)

CREATE TABLE JUL12_S_L_04(

SID NUMBER(4),

LID NUMBER(4),

SOURCE NUMBER(4)

);

INSERT INTO JUL12_S_L_04 VALUES (101,100,59);

INSERT INTO JUL12_S_L_04 VALUES (101,101,60);

INSERT INTO JUL12_S_L_04 VALUES (101,102,88);

INSERT INTO JUL12_S_L_04 VALUES (102,100,59);

INSERT INTO JUL12_S_L_04 VALUES (102,101,60);

INSERT INTO JUL12_S_L_04 VALUES (102,102,88);

INSERT INTO JUL12_S_L_04 VALUES (103,100,59);

INSERT INTO JUL12_S_L_04 VALUES (103,101,60);

INSERT INTO JUL12_S_L_04 VALUES (103,102,88);

INSERT INTO JUL12_S_L_04 VALUES (104,100,59);

INSERT INTO JUL12_S_L_04 VALUES (104,101,60);

INSERT INTO JUL12_S_L_04 VALUES (104,102,88);

CREATE TABLE JUL12_GRADE_04 (

LEVEL1 VARCHAR2(2),

LOW NUMBER(3),

HIGH NUMBER(3)

);

INSERT INTO JUL12_GRADE_04 VALUES('A',80,100);

INSERT INTO JUL12_GRADE_04 VALUES('B',50,80);

SELECT S.SNAME,G.LEVEL1 FROM JUL12_STUDENT_04 S,JUL12_S_L_04 SL,JUL12_GRADE_04 G WHERE S.SID =SL.SID AND SL.SOURCE BETWEEN G.LOW AND G.HIGH

SELECT S.SNAME,G.LEVEL1 ,L.LNAME

FROM JUL12_STUDENT_04 S,JUL12_S_L_04 SL,JUL12_GRADE_04 G ,JUL12_LESSION_04 L

WHERE (S.SID =SL.SID) AND (SL.SOURCE BETWEEN G.LOW AND G.HIGH)

－－自连接

SELECT SNAME

FROM JUL12_STUDENT_04 A,JUL12_STUDENT_04 B

WHERE (A.SNAME= B.SNAME) AND (A.SID!=B.SID)

－－外连接

SELECT SNAME,AGE,CNAME

FROM JUL12_CLASS_04 A, JUL12_STUDENT_04 B

WHERE A.CID=B.SID(+);

符号＋为为外连接，可以分为左外连接，和右外连接。

在少的一方给与加号。然后就可以显示多的一方的所有的内容。

－－group分组查询

GROUP BY

SELECT COUNT(*) FROM JUL12_STUDENT_04 GROUP BY TRUNC (AGE/10)

－－分组函数

SELECT AVG(AGE) FROM TABLEOFSTUDENT

COUNT(DISTINCT|ALL|EXPR|*)

MAX (DISTINCT|ALL|EXPR)

MIN (DISTINCT|ALL|EXPR)

SUM (DISTINCT|ALL|N)

SELECT COUNT(*) FROM JUL12_STUDENT_04

查询出年龄大于23，每个班机的人数

SELECT COUNT(*) FROM JUL12_STUDENT_04 WHERE AGE >13 GROUP BY CID;

SELECT COUNT(*),TRUNC(AGE/10) FROM JUL12_STUDENT_04 GROUP BY TRUNC(AGE/10);

ORDER BY 是可以使用函数的

SELECT COUNT(*) AGE FROM JUL12_STUDENT_04

GROUP BY AGE

ORDER BY COUNT(*);

不可将分组函数使用WHERE语句中

使用HAVING

对组的条件进行过滤

SELECT COUNT(*) AS AGES FROM JUL12_STUDENT_04

ORDER BY AGE

HAVING COUNT(*)>2

Subqueries子查询

把一个查询的结果嵌入在另一个查询的条件的值

列出大于平均年龄的人

SELECT SNAME FROM JUL12_STUDENT_04

WHERE SAGE > SELECT AVG(AGE)FROM JUL12_STUDENT_04;

查询参加考试学生的姓名

SELECT SNAME FROM JUL12_STUDENT_04

WHERE SID NOT IN (

SELECT SID FROM JUL12_S_L_04

WHERE SOURCE !=NULL

)

SELECT TOP 3 * FROM JUL12_STUDENT_04

WHERE SID NOT IN (SELECT TOP 3 SID FROM JUL12_STUDENT_04)

分页

ROWNUM为伪字段

SELECT * FROM JUL12_STUDENT_04 WHERE ROWNUM<6 获取前5列的内容

查询到当前数据库中的第三个数据和第四个数据。为以后的分页作准备。

SELECT * FROM JUL12_STUDENT_04

WHERE SID NOT IN (

SELECT SID FROM JUL12_STUDENT_04

WHERE ROWNUM <=3)

AND ROWNUM<=3;

SELECT SID ,SNAME FROM (

SELECT SID, SNAME, ROWNUM R

FROM JUL12_STUDENT_04

) WHERE R >=4 AND R<= 6

提高效率

SELECT SID,SNAME FROM(

SELECT SID ,SNAME,ROWNUM R

FROM JUL12_STUDENT_04 WHERE ROWNUM<=6)

WHERE R >=4;

SELECT SID, SNAME FROM(

SELECT SID,SNAME, ROWNUM R

FROM (

SELECT SID,SNAME FROM

JUL12_STUDENT_04

ORDER BY SID DESC

)

)

WHERE R >=4 AND R<= 6

SELECT SID,SNAME FROM(

SELECT SID,SNAME ,ROWNUM R

FROM(

SELECT * FROM JUL12_STUDENT_04 ORDER BY SID DESC)

WHERE ROWNUM <=6

)

WHERE R>=4;