Oracle 行列转置

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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 table1
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 table1;

也可以利用分析函数和 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;

建立一个自定义函数在查询中调用，如果行很多，每一行都要调用一次函数，性能非常差。用Oracle的分析函数结合递归语法也可以实现相同的功能，而且不会每行调用，性能好得多。

1. CREATE TABLE wm_test
2. (
3. code NUMBER,
4. name1 VARCHAR2 (100),
5. seq NUMBER
6. );
8. INSERT INTO wm_test
9. VALUES (1, 'a', 1);
11. INSERT INTO wm_test
12. VALUES (1, 'b', 2);
14. INSERT INTO wm_test
15. VALUES (1, 'c', 3);
17. INSERT INTO wm_test
18. VALUES (2, ' 中', 1);
20. INSERT INTO wm_test
21. VALUES (2, '国', 2);
23. INSERT INTO wm_test
24. VALUES (2, '人', 3);
26. COMMIT;
28. CREATE OR REPLACE VIEW v1
29. AS
30. SELECT code, name1
31. FROM (SELECT code,
32. name1,
33. ROW\_NUMBER ()
34. OVER (PARTITION **BY** code **ORDER** **BY** LENGTH (name1) **DESC**)
35. rn2
36. FROM ( SELECT code, SYS_CONNECT_BY_PATH (name1, '^') name1
37. FROM (SELECT code,
38. name1,
39. rn,
40. LEAD (rn)
41. OVER (PARTITION **BY** code **ORDER** **BY** rn)
42. rn1
43. FROM (SELECT code,
44. name1,
45. ROW\_NUMBER ()
46. OVER (**ORDER** **BY** code, seq **DESC**)
47. rn
48. FROM wm_test))
49. START **WITH** rn1 **IS** NULL
50. CONNECT BY rn1 = PRIOR rn))
51. WHERE rn2 = 1;
53. SELECT * FROM v1;

更简单的写法如下：

sql view plain copy

1. -- name1如果有顺序，则按照其seq排序
2. SELECT code, LTRIM (MAX (SYS_CONNECT_BY_PATH (name1, '^')), '^') name1
3. FROM wm_test
4. START WITH seq = 1
5. CONNECT BY seq = PRIOR seq + 1 AND code = PRIOR code
6. GROUP BY code;
8. -- name1如果没有顺序，则按照rowid排序
9. SELECT code, LTRIM (MAX (SYS_CONNECT_BY_PATH (name1, '^')), '^') name1
10. FROM (SELECT code,
11. name1,
12. ROW\_NUMBER () OVER (PARTITION **BY** code **ORDER** **BY** ROWID) rn1
13. FROM wm_test)
14. START WITH rn1 = 1
15. CONNECT BY rn1 = PRIOR rn1 + 1 AND code = PRIOR code
16. GROUP BY code;