第五章使用字符串

1.遍历字符串

SELECT '天天向上' 内容，level，substr('天天向上', LEVEL, 1) 汉字拆分
  FROM Dual
CONNECT BY LEVEL <= Length('天天向上');

2.计算字符在字符串中出现的次数

3.从字符中删除不需要的字符

若员工姓名有元音字母AEIOU，现在要求把这写元音字母去掉。

SELECT 'aAbcdef', Translate('abcdef', '1AEIOUaeiou', '1') FROM Dual;
SELECT 'aAbcdef', Regexp_Replace('abcdef', '[AEIOUaeiou]') FROM Dual;

将字符和数字数据分离也可以通过regexp_replace分离：

regexp_replace(data,'[0-9],'') 字符

regexp_replace(data,'[^0-9],'') 数字

4.正则表达式 regexp_like

4.1^和$的含义

4.2+和*的含义

4.3 ^和$与+和*联合使用

5.提取姓名的大写字母缩写

6.按字符串中的数值排序

7. 根据表中的行创建一个分割列表

SELECT Deptno,
       SUM(Sal) AS Total_Sal,
       Listagg(Ename, ',') Within GROUP(ORDER BY Ename) AS Total_Name
  FROM Emp
 GROUP BY Deptno;

8.提取第n个分隔的子串

--function REGEXP_SUBSTR(String, pattern, position, occurrence, modifier)
--参数二：-^在方括号里表示否的意思，+表示匹配1次以上，[^,]+表示匹配不包含逗号的多个字符。
--参数三：1表示从第一个字符开始。
--参数四：2表示第二个能匹配'[^,]+'的字符串。
--参数五：模式（‘i’不区分大小写进行检索；‘c’区分大小写进行检索。默认为’c’）针对的是正则表达式里字符大小写的匹配
SELECT Regexp_Substr(Total_Name, '[^,]+', 1, 2) AS 第二个子串
  FROM (SELECT Listagg(Ename, ',') Within GROUP(ORDER BY Ename) AS Total_Name
          FROM Emp);

9.分解IP的地址

--分解ip地址192.168.1.1
SELECT Regexp_Substr(Ip, '[^.]+', 1, 1) AS a,
Regexp_Substr(Ip, '[^.]+', 1, 2) AS b,
Regexp_Substr(Ip, '[^.]+', 1, 3) AS c,
Regexp_Substr(Ip, '[^.]+', 1, 4) AS d
  FROM (SELECT '192.168.1.1' AS Ip FROM Dual);

10.将分隔数据转换为多值in列表

DECLARE
  CURSOR c_Emps(v_Emps VARCHAR2) IS
    SELECT *
      FROM Emp
     WHERE Ename IN
           (SELECT Regexp_Substr(v_Emps, '[^,]+', 1, LEVEL) AS Ename
              FROM Dual
            CONNECT BY LEVEL <=
                       Length(Translate(v_Emps, ',' || v_Emps, ',')) + 1);

  c_Emp_Rec c_Emps%ROWTYPE;
BEGIN
  OPEN c_Emps('&InputString');
  LOOP
    FETCH c_Emps
      INTO c_Emp_Rec;
    EXIT WHEN c_Emps%NOTFOUND;
    Dbms_Output.Put_Line(c_Emp_Rec.Ename);
  END LOOP;

END;

11.按字母顺序排列字符串

SELECT Ename,
       (SELECT Listagg(Substr(Ename, LEVEL, 1))
           Within GROUP(ORDER BY Substr(Ename, LEVEL, 1))
          FROM Dual
        CONNECT BY LEVEL <= Length(Ename)) AS New_Name
  FROM Emp;

SELECT Ename,
       (SELECT Listagg(min(Substr(Ename, LEVEL, 1)))
        Within GROUP(ORDER BY (Substr(Ename, LEVEL, 1)))
          FROM Dual
        CONNECT BY LEVEL <= Length(Ename) 
        GROUP BY Substr(Ename, LEVEL, 1)) AS New_Name
  FROM Emp;