Oracle 伪列Level的应用

目录导航：

1. 根据ID的数量按序展开

2. 根据ID的数量按序展开

3. 生成随机数

4. 转置截取字符串

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1、根据ID的数量按序展开

WITH TB AS
 (SELECT 'U101' USER_ID, DATE '2016-11-02' START_DT, DATE '2016-11-06' END_DT
    FROM DUAL
  UNION ALL
  SELECT 'U102', DATE '2015-06-01', DATE '2015-06-03' FROM DUAL)
SELECT TB.USER_ID, TB.START_DT + LEVEL - 1
  FROM TB
CONNECT BY TB.USER_ID = PRIOR TB.USER_ID
       AND LEVEL <= (TB.END_DT - TB.START_DT + 1)
       AND PRIOR DBMS_RANDOM.VALUE IS NOT NULL;

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2. 根据ID的数量按序展开

WITH TB AS
 (SELECT 'U101' USER_ID, '12345' MOBILE, 3 CNT
    FROM DUAL
  UNION ALL
  SELECT 'U102', '33563', 4 FROM DUAL)
SELECT A.USER_ID, A.MOBILE, B.LV
  FROM TB A
  LEFT JOIN (SELECT TB.USER_ID, LEVEL LV
               FROM TB
             CONNECT BY TB.USER_ID = PRIOR TB.USER_ID
                    AND LEVEL <= CNT
                    AND PRIOR DBMS_RANDOM.VALUE IS NOT NULL) B
    ON A.USER_ID = B.USER_ID

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3. 生成随机数

SELECT DBMS_RANDOM.VALUE
  FROM DUAL 
  CONNECT BY LEVEL <= 100;

SELECT SYSDATE - LEVEL
  FROM DUAL 
  CONNECT BY LEVEL <= 100;

 SELECT TO_DATE('2020/01/02 08:00:00', 'yyyy-MM-dd HH24:mi:ss') +
         (LEVEL - 1) DT
   FROM DUAL
 CONNECT BY LEVEL <= 7;

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4. 转置截取字符串

 SELECT SUBSTR('大家好', LEVEL, 1)
   FROM DUAL
 CONNECT BY LEVEL <= LENGTH('大家好');

 WITH TB AS
  (SELECT 'U1' USER_ID, '哈喽,世界' STR
     FROM DUAL
   UNION ALL
   SELECT 'U2', '你好啊,地球' FROM DUAL)
 SELECT TB.USER_ID, SUBSTR(STR, LEVEL, 1)
   FROM TB
 CONNECT BY TB.USER_ID = PRIOR TB.USER_ID
        AND LEVEL <= LENGTH(STR)
        AND PRIOR DBMS_RANDOM.VALUE IS NOT NULL;

WITH tb AS
 (SELECT 'a' rn, '1,2,3' i_name
    FROM dual
  UNION ALL
  SELECT 'b', '4,5,6' FROM dual)
SELECT rn, regexp_substr(i_name, '[^,]+', 1, LEVEL)
  FROM tb
CONNECT BY PRIOR dbms_random.value IS NOT NULL
       AND PRIOR rn = rn
       AND LEVEL <= length(i_name) - length(REPLACE(i_name, ',', '')) + 1;