Oracle之縱向數據轉換橫向數據

1、固定列數的行列轉換
如
student subject grade
--------- ---------- --------
student1 語文 80
student1 數學 70
student1 英語 60
student2 語文 90
student2 數學 80
student2 英語 100
……
轉換為
語文 數學 英語
student1 80 70 60
student2 90 80 100
……
語句如下：select student, 
sum(decode(subject,'語文', grade,null)) "語文",
sum(decode(subject,'數學', grade,null)) "數學",
sum(decode(subject,'英語', grade,null)) "英語"
from table
group by student;
　

2、不定列行列轉換
如
c1 c2
--- -----------
1 我
1 是
1 誰
2 知
2 道
3 不
……
轉換為
1 我是誰
2 知道
3 不

這一類型的轉換可以借助於PL/SQL來完成，這里給一個例子
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，利用分析函數和 CONNECT_BY 實現：

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、列數不固定（交叉表行列轉置）
這種是比較麻煩的一種，需要借助pl/sql：

原始數據：
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

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

試驗如下：
1）. 建立測試表和數據
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准備輸出結果集 
CREATE OR REPLACE PACKAGE pkg_getrecord
IS
    TYPE myrctype IS REF CURSOR;
END pkg_getrecord;
/

3）. 建立動態sql交叉表函數，輸出結果集 
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）. 測試在sql plus下執行：
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