DB2行列轉置之行轉列

建表，並insert 2行資料
CREATE TABLE SalesAgg(year INTEGER, q1 INTEGER, q2 INTEGER, q3 INTEGER, q4 INTEGER);
insert into SalesAgg values(2004,20,30,15,10);
insert into SalesAgg values(2005,18,40,12,27);

Select * from SalesAgg

 YEAR Q1 Q2 Q3 Q4
 ---- -- -- -- --
 2004 20 30 15 10
 2005 18 40 12 27

想把資料轉成下面的樣子
 YEAR QUARTER RESULTS
 ---- ------- -------
 2004       1      20
 2004       2      30
 2004       3      15
 2004       4      10
 2005       1      18
 2005       2      40
 2005       3      12
 2005       4      27

列轉換成行的SQL
SELECT Year, Quarter, Results
FROM SalesAgg AS S,
LATERAL(VALUES(1, S.q1),
(2, S.q2),
(3, S.q3),
(4, S.q4))
AS Q(Quarter, Results);


LATERAL的地方可以換成TABLE，結果一樣，其目的都是透過VALUES值來組合成一個臨時表Q在SQL中使用
SELECT Year, Quarter, Results
FROM SalesAgg AS S,
TABLE(VALUES(1, S.q1),
(2, S.q2),
(3, S.q3),
(4, S.q4))
AS Q(Quarter, Results);

另外一個使用TABLE的例子
SELECT id ANSWER
    ,salary AS sal
    ,comm AS com
    ,combo
    ,typ
FROM staff
    ,TABLE (
        VALUES (
            salary
            ,'SAL'
            )
            ,(
            comm
            ,'COM'
            )
        ) AS tab(combo, typ)
WHERE id < 40
ORDER BY id
    ,typ;                   

行轉列使用示例

CREATE OR REPLACE PROCEDURE DB2INST1.TEST(OUT out_msg VARCHAR(4000))
SPECIFIC DB2INST1.TEST
MODIFIES SQL DATA
NOT DETERMINISTIC
NULL CALL
LANGUAGE SQL EXTERNAL ACTION
INHERIT SPECIAL REGISTERS
BEGIN
    DECLARE v_col1s VARCHAR(4000);
    DECLARE v_sql VARCHAR(4000);
    SELECT SUBSTR(XMLCAST(XMLGROUP(',' || col1 AS a ORDER BY col1) as varchar(4000)),2) into v_col1s FROM aaa;
    SET out_msg = 'SELECT * FROM aaa where col1 in (' || TRIM(v_col1s) || ')';     
END@