Oracle中行列互换有哪些方法？
♣ 答案部分
行列转换包括以下六种情况：（1）列转行。（2）行转列。（3）多列转换成字符串。（4）多行转换成字符串。（5）字符串转换成多列。（6）字符串转换成多行。其中，重点是行转列和字符串转换成多行。
下面将分别对这几种情况举例来说明。
1、列转行
列转行就是将原表中的列名作为转换后的表的内容。列转行主要采用UNION ALL来完成。示例代码如下所示：
CREATE TABLE TEST_LHR
(
NAME VARCHAR2(255),
JANUARY NUMBER(18),
FEBRUARY NUMBER(18),
MARCH NUMBER(18),
APRIL NUMBER(18),
MAY NUMBER(18)
);
INSERT INTO TEST_LHR (NAME, JANUARY, FEBRUARY, MARCH, APRIL, MAY)
VALUES ('长寿', 58, 12, 26, 18, 269);
INSERT INTO TEST_LHR (NAME, JANUARY, FEBRUARY, MARCH, APRIL, MAY)
VALUES ('璧山', 33, 18, 17, 16, 206);
INSERT INTO TEST_LHR (NAME, JANUARY, FEBRUARY, MARCH, APRIL, MAY)
VALUES ('杨家坪', 72, 73, 79, 386, 327);
INSERT INTO TEST_LHR (NAME, JANUARY, FEBRUARY, MARCH, APRIL, MAY)
VALUES ('巫溪', 34, 9, 7, 21, 33);
INSERT INTO TEST_LHR (NAME, JANUARY, FEBRUARY, MARCH, APRIL, MAY)
VALUES ('丰都', 62, 46, 39, 36, 91);
INSERT INTO TEST_LHR (NAME, JANUARY, FEBRUARY, MARCH, APRIL, MAY)
VALUES ('武隆', 136, 86, 44, 52, 142);
COMMIT;
SELECT * FROM TEST_LHR;
下面进行列转换：
SELECT *
FROM (SELECT T.NAME, 'JANUARY' MONTH, T.JANUARY V_NUM
FROM TEST_LHR T
UNION ALL
SELECT T.NAME, 'FEBRUARY' MONTH, T.FEBRUARY V_NUM
FROM TEST_LHR T
UNION ALL
SELECT T.NAME, 'MARCH' MONTH, T.MARCH V_NUM
FROM TEST_LHR T
UNION ALL
SELECT T.NAME, 'APRIL' MONTH, T.APRIL V_NUM
FROM TEST_LHR T
UNION ALL
SELECT T.NAME, 'MAY' MONTH, T.MAY V_NUM
FROM TEST_LHR T)
ORDER BY NAME;
2、行转列
行转列就是将行数据内容作为列名。示例代码如下所示：
CREATE TABLE T_ROW_COL_LHR(
NUM VARCHAR2(15 CHAR),
NAME VARCHAR2(20 CHAR),
SEX VARCHAR2(2 CHAR),
CLASSES VARCHAR2(30 CHAR),
COURSE_NAME VARCHAR2(50 CHAR)
);
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206211','王艺','男','06-1班','保险学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206212','肖薇','女','06-2','保险学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206212','肖薇','女','06-2','财务管理');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206212','肖薇','女','06-2','财务会计');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206213','陈雅诗','女','06-2','电子商务');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206213','陈雅诗','女','06-2','公共经济学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206213','陈雅诗','女','06-2','公司理财');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206213','陈雅诗','女','06-2','管理学原理');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206213','陈雅诗','女','06-2','保险学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206214','李丹阳','男','06-1','保险学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206214','李丹阳','男','06-1','财务管理');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206214','李丹阳','男','06-1','财务会计');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206214','李丹阳','男','06-1','电子商务');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206214','李丹阳','男','06-1','公共经济学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206215','杨伊琳','女','06-3班','环境管理学');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206215','杨伊琳','女','06-3班','管理学原理');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206215','杨伊琳','女','06-3班','商务谈判');
INSERT INTO T_ROW_COL_LHR(NUM,NAME,SEX,CLASSES,COURSE_NAME) VALUES ('206216','李佳琪','男','06-2','土地估计');
SELECT * FROM T_ROW_COL_LHR;
将COURSE_NAME进行行转列：
SELECT NUM,NAME,SEX,CLASSES,
MAX(DECODE(RN,1,COURSE_NAME,NULL)) COURSE_NAME_1,
MAX(DECODE(RN,2,COURSE_NAME,NULL)) COURSE_NAME_2,
MAX(DECODE(RN,3,COURSE_NAME,NULL)) COURSE_NAME_3,
MAX(DECODE(RN,4,COURSE_NAME,NULL)) COURSE_NAME_4,
MAX(DECODE(RN,5,COURSE_NAME,NULL)) COURSE_NAME_5
FROM (SELECT NUM,NAME,SEX,CLASSES,COURSE_NAME,
ROW_NUMBER() OVER(PARTITION BY NUM,NAME,SEX,CLASSES ORDER BY COURSE_NAME) RN
FROM T_ROW_COL_LHR)
GROUP BY NUM,NAME,SEX,CLASSES;
结果如下所示：
将COURSE_NAME列合并，示例代码如下所示：
SELECT NUM,
NAME,
SEX,
CLASSES,
(MAX(DECODE(RN, 1, COURSE_NAME, NULL)) ||
MAX(DECODE(RN, 2, ',' || COURSE_NAME, NULL)) ||
MAX(DECODE(RN, 3, ',' || COURSE_NAME, NULL)) ||
MAX(DECODE(RN, 4, ',' || COURSE_NAME, NULL)) ||
MAX(DECODE(RN, 5, ',' || COURSE_NAME, NULL))) NAME
FROM (SELECT NUM,
NAME,
SEX,
CLASSES,
COURSE_NAME,
ROW_NUMBER() OVER(PARTITION BY NUM, NAME, SEX, CLASSES ORDER BY COURSE_NAME) RN
FROM T_ROW_COL_LHR)
GROUP BY NUM,
NAME,
SEX,
CLASSES;
结果如下所示：
3、多列转换成字符串
使用||或CONCAT函数实现。示例代码如下所示。
SELECT CONCAT('A','B') FROM DUAL;
4、多行转换成字符串
示例代码如下所示：
CREATE TABLE T_ROW_STR(
ID INT,
COL VARCHAR2(10)
);
INSERT INTO T_ROW_STR VALUES(1,'A');
INSERT INTO T_ROW_STR VALUES(1,'B');
INSERT INTO T_ROW_STR VALUES(1,'C');
INSERT INTO T_ROW_STR VALUES(2,'A');
INSERT INTO T_ROW_STR VALUES(2,'D');
INSERT INTO T_ROW_STR VALUES(2,'E');
INSERT INTO T_ROW_STR VALUES(3,'C');
COMMIT;
SELECT * FROM T_ROW_STR;
SELECT ID,
MAX(DECODE(RN, 1, COL, NULL)) ||
MAX(DECODE(RN, 2, ',' || COL, NULL)) ||
MAX(DECODE(RN, 3, ',' || COL, NULL)) STR
FROM (SELECT ID,
COL,
ROW_NUMBER() OVER(PARTITION BY ID ORDER BY COL) AS RN
FROM T_ROW_STR) T
GROUP BY ID
ORDER BY 1;
也可以使用SYS_CONNECT_BY_PATH来实现：
SELECT T.ID ID,
MAX(SUBSTR(SYS_CONNECT_BY_PATH(T.COL, ','), 2)) STR
FROM (SELECT ID,
COL,
ROW_NUMBER() OVER(PARTITION BY ID ORDER BY COL) RN
FROM T_ROW_STR) T
START WITH RN = 1
CONNECT BY RN = PRIOR RN + 1
AND ID = PRIOR ID
GROUP BY T.ID;
5、字符串转换成多列
实际上就是一个字符串拆分的问题。示例代码如下所示：
CREATE TABLE T_COL_ROW(
ID INT,
C1 VARCHAR2(10),
C2 VARCHAR2(10),
C3 VARCHAR2(10));
INSERT INTO T_COL_ROW VALUES (1, 'v11', 'v21', 'v31');
INSERT INTO T_COL_ROW VALUES (2, 'v12', 'v22', NULL);
INSERT INTO T_COL_ROW VALUES (3, 'v13', NULL, 'v33');
INSERT INTO T_COL_ROW VALUES (4, NULL, 'v24', 'v34');
INSERT INTO T_COL_ROW VALUES (5, 'v15', NULL, NULL);
INSERT INTO T_COL_ROW VALUES (6, NULL, NULL, 'v35');
INSERT INTO T_COL_ROW VALUES (7, NULL, NULL, NULL);
COMMIT;
SELECT * FROM T_COL_ROW;
CREATE TABLE T_STR_COL AS
SELECT ID,C1||','||C2||','||C3 AS C123
FROM T_COL_ROW;
SELECT * FROM T_STR_COL;
SELECT ID,
C123,
SUBSTR(C123, 1, INSTR(C123 || ',', ',', 1, 1) - 1) C1,
SUBSTR(C123,
INSTR(C123 || ',', ',', 1, 1) + 1,
INSTR(C123 || ',', ',', 1, 2) - INSTR(C123 || ',', ',', 1, 1) - 1) C2,
SUBSTR(C123,
INSTR(C123 || ',', ',', 1, 2) + 1,
INSTR(C123 || ',', ',', 1, 3) - INSTR(C123 || ',', ',', 1, 2) - 1) C3
FROM T_STR_COL
ORDER BY 1;
6、字符串转换成多行
示例代码如下所示：
CREATE TABLE T_STR_ROW AS
SELECT ID,
MAX(DECODE(RN, 1, COL, NULL)) ||
MAX(DECODE(RN, 2, ',' || COL, NULL)) ||
MAX(DECODE(RN, 3, ',' || COL, NULL)) STR
FROM (SELECT ID,
COL,
ROW_NUMBER() OVER(PARTITION BY ID ORDER BY COL) AS RN
FROM T_ROW_STR) T
GROUP BY ID
ORDER BY 1;
SELECT * FROM T_STR_ROW;
SELECT ID,
1 AS P,
SUBSTR(STR, 1, INSTR(STR || ',', ',', 1, 1) - 1) AS CV
FROM T_STR_ROW
UNION ALL
SELECT ID,
2 AS P,
SUBSTR(STR,
INSTR(STR || ',', ',', 1, 1) + 1,
INSTR(STR || ',', ',', 1, 2) - INSTR(STR || ',', ',', 1, 1) - 1) AS CV
FROM T_STR_ROW
UNION ALL
SELECT ID,
3 AS P,
SUBSTR(STR,
INSTR(STR || ',', ',', 1, 1) + 1,
INSTR(STR || ',', ',', 1, 2) - INSTR(STR || ',', ',', 1, 1) - 1) AS CV
FROM T_STR_ROW
ORDER BY 1,
2;
还有几类特殊的转换，如下所示：
CREATE OR REPLACE TYPE INS_SEQ_TYPE IS VARRAY(8) OF NUMBER;
SELECT * FROM TABLE(INS_SEQ_TYPE(1, 2, 3, 4, 5));
结果：
COLUMN_VALUE
------------
1
2
3
4
5
若是字符串类型，则如下所示：
CREATE OR REPLACE TYPE INS_SEQ_TYPE2 IS VARRAY(80) OF VARCHAR2(32767);
SELECT * FROM TABLE(INS_SEQ_TYPE2('aadf,dea','cbc','d'));
结果：
COLUMN_VALUE
-----------------
aadf,dea
cbc
d
还有如下的形式：
先创建一个TYPE类型，代码如下：
CREATE OR REPLACE TYPE TYPE_STR_LHR IS TABLE OF VARCHAR2(32767);
再创建FUN_SPLIT2_LHR函数，代码如下：
CREATE OR REPLACE FUNCTION FUN_SPLIT2_LHR(P_STR VARCHAR2,
V_SPLIT VARCHAR2 DEFAULT ',') RETURN TYPE_STR_LHR IS
RS TYPE_STR_LHR := TYPE_STR_LHR();
V_STR VARCHAR2(4000) := '';
V_LEN NUMBER := 0;
BEGIN
V_STR := P_STR;
V_LEN := LENGTH(V_SPLIT);
WHILE LENGTH(V_STR) > 0 LOOP
IF INSTR(V_STR, V_SPLIT) > 0 THEN
RS.EXTEND;
RS(RS.COUNT) := SUBSTR(V_STR, 1, INSTR(V_STR, V_SPLIT) - 1);
V_STR := SUBSTR(V_STR, INSTR(V_STR, V_SPLIT) + V_LEN);
ELSE
RS.EXTEND;
RS(RS.COUNT) := V_STR;
EXIT;
END IF;
END LOOP;
RETURN RS;
END;
测试如下：
SQL> SELECT COLUMN_VALUE FROM TABLE(FUN_SPLIT2_LHR('101,102,103',','));
COLUMN_VALUE
------------------
101
102
103
SQL> SELECT TO_NUMBER(COLUMN_VALUE) FROM TABLE(FUN_SPLIT2_LHR('101,102,103'));
TO_NUMBER(COLUMN_VALUE)
-----------------------
101
102
103
SQL> SELECT COLUMN_VALUE FROM TABLE(FUN_SPLIT2_LHR('101@#102@#103','@#'));
COLUMN_VALUE
---------------
101
102
103
& 说明：
有关行列互换更多的案例可以参考我的BLOG：http://blog.itpub.net/26736162/viewspace-1272538/
本文选自《Oracle程序员面试笔试宝典》，作者：李华荣。
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