Oracle—decode函数行转列

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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));

2、给三张表插入相应的数据

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          2220141102   MARY                                               GIRL         2220141103   SILLY                                              GIRL         2220141104   ALICE                                              GIRL         2220141105   SAM                                                BOY          22COURSEID   COURSENAME TEACHER---------- ---------- ----------1001       MATH       SA1002       ENGLISH    ALICE1003       JAVA       BBSCOREID    COURSEID   STUDENTID        GRADE---------- ---------- ---------- -----------10001      1001       20041101            9910002      1001       20041102            8810003      1001       20041103            7710004      1001       20041104            9810005      1001       20041105            9610006      1002       20041101            9910007      1002       20041103            9910008      1002       20041104            9910009      1003       20041102            9910010      1003       20041105            99

3、对数据进行行转列操作

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)) javafrom tb_score ggroup by g.studentidorder by g.studentid;

说明：decode函数除了可以进行数据匹配以外，还可以进行行转列的功能

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          020141102   MARY                                                       88          0         9920141103   SILLY                                                      77         99          020141104   ALICE                                                      98         99          020141105   SAM                                                        96          0         99

以上是通过oracle的decode函数进行的行转列操作，初次写博文，多多指教！

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