使用 Oracle：我可以在 pivot 子句中使用“动态”创建的变量吗？

Question

我正在尝试创建从变量中获取参数的数据透视子句。

我有一些测试代码，例如：

SELECT * FROM (
SELECT U.USER_ID, U.USER_NAME, E.EXAM_ID, EU.EXAM_DATE
FROM USERS U, EXAMS E, EXAM_USER EU
WHERE U.USER_ID = EU.USER_ID(+)
AND E.EXAM_ID(+) = EU.EXAM_ID
ORDER BY U.USER_ID
  )
  PIVOT (MAX(EXAM_DATE) FOR EXAM_ID IN ('3' AS "exam 3",'2' AS "exam 2",'1' AS "exam 1"))
  order by 1
;

这很好用。然后我将变量 EXAM_IDS 声明为：

DECLARE
  EXAM_IDS VARCHAR2 (255);
BEGIN
  SELECT LISTAGG('''' || EXAM_ID || ''' AS "' || EXAM_NAME || '"', ',')
  WITHIN GROUP (ORDER BY EXAM_ID DESC) 
  INTO EXAM_IDS
  FROM EXAMS;
END;

我很确定变量 EXAM_IDS 现在有一个字符串，用于枢轴子句（？），但我不知道如何将这两者结合起来：

DECLARE
  EXAM_IDS VARCHAR2 (255);
BEGIN
  SELECT LISTAGG('''' || EXAM_ID || ''' AS "' || EXAM_NAME || '"', ',')
  WITHIN GROUP (ORDER BY EXAM_ID DESC) 
  INTO EXAM_IDS
  FROM EXAMS;
END;

SELECT * FROM (
SELECT U.USER_ID, U.USER_NAME, E.EXAM_ID, EU.EXAM_DATE
FROM USERS U, EXAMS E, EXAM_USER EU
WHERE U.USER_ID = EU.USER_ID(+)
AND E.EXAM_ID(+) = EU.EXAM_ID
ORDER BY U.USER_ID
  )
  PIVOT (MAX(EXAM_DATE) FOR EXAM_ID IN (' || EXAM_IDS || '))
  order by 1
;

这不起作用。有没有办法做到这一点，或者我应该只运行两个单独的 SQL 查询？

可以从Using Oracle combine three tables to one with PIVOT找到有关此设置的更多信息（例如我的课程）

Answer 1

对于 12c 及更高版本，您可以通过为动态 PIVOT 查询打开 REFCURSOR 来使用 DBMS_SQL.RETURN_RESULT。

我已经为 left join 删除了臭名昭著的 (+) 语法，始终使用 ANSI join 语法。

DECLARE
    exam_ids   VARCHAR2(255);
    x          SYS_REFCURSOR;
BEGIN
    SELECT
        LISTAGG(''''
                  || exam_id
                  || ''' AS "'
                  || exam_name
                  || '"',',') WITHIN GROUP(
            ORDER BY
                exam_id DESC
        )
    INTO exam_ids
    FROM
        exam;

    OPEN x FOR 'SELECT
        *
               FROM
        (
            SELECT
                u.user_id,
                u.user_name,
                e.exam_id,
                eu.exam_date
            FROM
                users u
                LEFT JOIN exam_user eu ON u.user_id = eu.user_id
                LEFT JOIN exam e ON e.exam_id = eu.exam_id
            ORDER BY
                u.user_id
        )
            PIVOT ( MAX ( exam_date )
                FOR exam_id
                IN ( ' || EXAM_IDS || ' )
            )
    ORDER BY
        1';

    dbms_sql.return_result(x);
END;
/

对于 11g，您可以使用绑定变量和 print 命令（在 sqlplus 和 sql developer/Toad 作为脚本运行时工作 (F5)）

variable x REFCURSOR  -- bind variable declared.
DECLARE
    ..   -- no need to declare sys_refcursor
BEGIN
     ..

    OPEN :x FOR 'SELECT . --note the change with colon
        *
               FROM
        (
            SELECT
            ..

END;
/


print x