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;

---

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

---

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;

---

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;