总结一下关于行列转置的实现方法

这是行转列问题，CSDN的一位版主发的，感觉经典。所以收藏了！

总结一下关于行列转置的实现方法
1、固定列数的行列转换
如
student subject grade
--------- ---------- --------
student1 语文 80
student1 数学 70
student1 英语 60
student2 语文 90
student2 数学 80
student2 英语 100
……
转换为
语文 数学 英语
student1 80 70 60
student2 90 80 100
……
语句如下：select student, 
sum(decode(subject,'语文', grade,null)) "语文",
sum(decode(subject,'数学', grade,null)) "数学",
sum(decode(subject,'英语', grade,null)) "英语"
from table
group by student;
　

2、不定列行列转换
如
c1 c2
--- -----------
1 我
1 是
1 谁
2 知
2 道
3 不
……
转换为
1 我是谁
2 知道
3 不

这一类型的转换可以借助于PL/SQL来完成，这里给一个例子
CREATE OR REPLACE FUNCTION get_c2(tmp_c1 NUMBER)
RETURN VARCHAR2
IS
Col_c2 VARCHAR2(4000);
BEGIN
FOR cur IN (SELECT c2 FROM t WHERE c1=tmp_c1) LOOP
Col_c2 := Col_c2||cur.c2;
END LOOP;
Col_c2 := rtrim(Col_c2,1);
RETURN Col_c2;
END;

select distinct c1 ,get_c2(c1) cc2 from table;


或者不用pl/sql，利用分析函数和 CONNECT_BY 实现：

SELECT c1, SUBSTR (MAX (SYS_CONNECT_BY_PATH (c2, ';')), 2) NAME
    FROM (SELECT c1, c2, rn, LEAD (rn) OVER (PARTITION BY c1 ORDER BY rn) rn1
            FROM (SELECT c1, c2, ROW_NUMBER () OVER (ORDER BY c2) rn
                    FROM t))
START WITH rn1 IS NULL
CONNECT BY rn1 = PRIOR rn
GROUP BY c1;


3、列数不固定（交叉表行列转置）
这种是比较麻烦的一种，需要借助pl/sql：

原始数据：
CLASS1     CALLDATE         CALLCOUNT
1          2005-08-08       40
1          2005-08-07       6
2          2005-08-08       77
3          2005-08-09       33
3          2005-08-08       9
3          2005-08-07       21

转置后：
CALLDATE     CallCount1 CallCount2 CallCount3
------------ ---------- ---------- ----------
2005-08-09   0          0          33
2005-08-08   40         77         9
2005-08-07 　6 　　　　　0          21

试验如下：
1）. 建立测试表和数据
CREATE TABLE t(
    class1 VARCHAR2(2 BYTE),
    calldate DATE,
    callcount INTEGER
);

INSERT INTO t(class1, calldate, callcount)
VALUES ('1', TO_DATE ('08/08/2005', 'MM/DD/YYYY'), 40);

INSERT INTO t(class1, calldate, callcount)
VALUES ('1', TO_DATE ('08/07/2005', 'MM/DD/YYYY'), 6);

INSERT INTO t(class1, calldate, callcount)
VALUES ('2', TO_DATE ('08/08/2005', 'MM/DD/YYYY'), 77);

INSERT INTO t(class1, calldate, callcount)
VALUES ('3', TO_DATE ('08/09/2005', 'MM/DD/YYYY'), 33);

INSERT INTO t(class1, calldate, callcount)
VALUES ('3', TO_DATE ('08/08/2005', 'MM/DD/YYYY'), 9);

INSERT INTO t(class1, calldate, callcount)
VALUES ('3', TO_DATE ('08/07/2005', 'MM/DD/YYYY'), 21); 

COMMIT ; 

2）. 建立ref cursor准备输出结果集 
CREATE OR REPLACE PACKAGE pkg_getrecord
IS
    TYPE myrctype IS REF CURSOR;
END pkg_getrecord;
/

3）. 建立动态sql交叉表函数，输出结果集 
CREATE OR REPLACE FUNCTION fn_rs
    RETURN pkg_getrecord.myrctype
IS
    s VARCHAR2 (4000); 
    CURSOR c1 IS
    SELECT ',sum(case when Class1='
            || class1
            || ' then CallCount else 0 end)'
            || ' "CallCount'
            || class1
            || '"' c2
    FROM t
    GROUP BY class1;
    r1 c1%ROWTYPE;
    list_cursor pkg_getrecord.myrctype;
BEGIN
    s := 'select CallDate ';
    OPEN c1;
    LOOP
        FETCH c1 INTO r1;
        EXIT WHEN c1%NOTFOUND;
        s := s || r1.c2;
    END LOOP;
    CLOSE c1;
    s := s || ' from T group by CallDate order by CallDate desc ';
    OPEN list_cursor FOR s;
    RETURN list_cursor;
END fn_rs;
/ 

4）. 测试在sql plus下执行：
var results refcursor;
exec :results := fn_rs;
print results;
CALLDATE        CallCount1 CallCount2 CallCount3
--------------- ---------- ---------- ----------
2005-08-09      0          0          33
2005-08-08      40         77         9
2005-08-07      6          0          21