Oracle—decode函数行转列

文章说明：根据成绩表，对每个学生的成绩数据进项行转列操作，最后每行显示每个学生的各科成绩。 以下是行转列的各个步骤操作。 1、创建学生信息，课程，成绩三张表 CREATE TABLE TB_STUDENT( STUDENTID VARCHAR2(10) PRIMARY KEY, STUNAME VARCHAR2(50), SE

文章说明：根据成绩表，对每个学生的成绩数据进项行转列操作，最后每行显示每个学生的各科成绩。

以下是行转列的各个步骤操作。

1、创建学生信息，课程，成绩三张表

CREATE TABLE TB_STUDENT(
       STUDENTID VARCHAR2(10) PRIMARY KEY,
       STUNAME VARCHAR2(50),
       SEX VARCHAR2(8),
       AGE NUMBER(5) 
);

CREATE TABLE TB_COURSE(
       COURSEID VARCHAR2(10) PRIMARY KEY,
       COURSENAME VARCHAR2(10),
       TEACHER VARCHAR2(10)
);

CREATE TABLE TB_SCORE(
       SCOREID VARCHAR2(10) PRIMARY KEY,
       COURSEID VARCHAR2(10),
       STUDENTID VARCHAR2(10),
       GRADE NUMBER(10)
);

INSERT INTO TB_STUDENT(STUDENTID,STUNAME,SEX,AGE) VALUES('20141101','SIM','BOY',22);
INSERT INTO TB_STUDENT(STUDENTID,STUNAME,SEX,AGE) VALUES('20141102','MARY','GIRL',22);
INSERT INTO TB_STUDENT(STUDENTID,STUNAME,SEX,AGE) VALUES('20141103','SILLY','GIRL',22);
INSERT INTO TB_STUDENT(STUDENTID,STUNAME,SEX,AGE) VALUES('20141104','ALICE','GIRL',22);
INSERT INTO TB_STUDENT(STUDENTID,STUNAME,SEX,AGE) VALUES('20141105','SAM','BOY',22);

insert into tb_course(COURSEID,coursename,teacher) VALUES('1001','MATH','SA');
insert into tb_course(COURSEID,coursename,teacher) VALUES('1002','ENGLISH','ALICE');
insert into tb_course(COURSEID,coursename,teacher) VALUES('1003','JAVA','BB');

INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10001','1001','20141101',99);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10002','1001','20141102',88);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10003','1001','20141103',77);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10004','1001','20141104',98);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10005','1001','20141105',96);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10006','1002','20141101',99);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10007','1002','20141103',99);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10008','1002','20141104',99);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10009','1003','20141102',99);
INSERT INTO TB_SCORE(SCOREID,COURSEID,STUDENTID,GRADE) VALUES('10010','1003','20141105',99);

插入后的数据结果如下：

STUDENTID  STUNAME                                            SEX         AGE
---------- -------------------------------------------------- -------- ------
20141101   SIM                                                BOY          22
20141102   MARY                                               GIRL         22
20141103   SILLY                                              GIRL         22
20141104   ALICE                                              GIRL         22
20141105   SAM                                                BOY          22


COURSEID   COURSENAME TEACHER
---------- ---------- ----------
1001       MATH       SA
1002       ENGLISH    ALICE
1003       JAVA       BB


SCOREID    COURSEID   STUDENTID        GRADE
---------- ---------- ---------- -----------
10001      1001       20041101            99
10002      1001       20041102            88
10003      1001       20041103            77
10004      1001       20041104            98
10005      1001       20041105            96
10006      1002       20041101            99
10007      1002       20041103            99
10008      1002       20041104            99
10009      1003       20041102            99
10010      1003       20041105            99

select g.studentid 学号,(select stu.stuname from tb_student stu where stu.studentid=g.studentid) AS 姓名,
sum(decode(g.courseid,'1001',grade,0)) 数学,
sum(decode(g.courseid,'1002',grade,0)) 英语,
sum(decode(g.courseid,'1003',grade,0)) java
from tb_score g
group by g.studentid
order by g.studentid;

decode函数格式：decode(column,if1,then1,defalut)

表示列如果满足if1的条件，就显示then1的内容，不满足就显示default的值！

sum(decode(...))是对decode返回的数据进行累加

4、通过上面的查询，最后显示的查询结果如下

学号       姓名                                                       数学         英语       JAVA
---------- -------------------------------------------------- ---------- ---------- ----------
20141101   SIM                                                        99         99          0
20141102   MARY                                                       88          0         99
20141103   SILLY                                                      77         99          0
20141104   ALICE                                                      98         99          0
20141105   SAM                                                        96          0         99