根据输入的用户ID串，返回用户名字串:TRIM函数的使用

建立表:

create table USER_INFO
(
  user_name VARCHAR2(100),
  id        VARCHAR2(32)
)

插入数据

insert into USER_INFO (USER_NAME, ID)
values ('小明', '1');

insert into USER_INFO (USER_NAME, ID)
values ('小刚', '3');

insert into USER_INFO (USER_NAME, ID)
values ('小陈', '4');

insert into USER_INFO (USER_NAME, ID)
values ('小红', '2');

建立函数，根据ID获取名字:

CREATE OR REPLACE FUNCTION GETUSERNAMEBYID(I_ID VARCHAR2) RETURN VARCHAR2 IS
  V_SQL       VARCHAR2(100);
  V_USER_NAME VARCHAR2(100);
BEGIN
  IF I_ID IS NULL THEN
    RETURN '';
  END IF;
  SELECT USER_NAME INTO V_USER_NAME FROM USER_INFO U WHERE U.ID = I_ID;
  RETURN V_USER_NAME;
EXCEPTION
  WHEN OTHERS THEN
    RETURN '';
END;

传入ID串，返回名字串

CREATE OR REPLACE FUNCTION GET_USER_NAMES(I_IDS IN CLOB) RETURN CLOB IS
  V_IDS       CLOB;
  V_ID        VARCHAR2(32);
  V_USERNAMES CLOB;
  V_USERNAME  VARCHAR2(100);
BEGIN
  --判断是否为空
  IF I_IDS IS NULL THEN
    RETURN '';
  END IF;
  BEGIN
    --截掉空格
    V_IDS := TRIM(I_IDS);
    --判断末尾是否有逗号分隔符：添加逗号分隔符
    IF SUBSTR(I_IDS, LENGTH(I_IDS)) != ';' THEN
      V_IDS := V_IDS || ';';
    END IF;
    WHILE INSTR(V_IDS, ';') != 0 LOOP
      --截取第一个ID
      V_ID := SUBSTR(V_IDS, 1, INSTR(V_IDS, ';') - 1);
    
      --重新赋值
      V_IDS := SUBSTR(V_IDS, INSTR(V_IDS, ';') + 1);
    
      DBMS_OUTPUT.PUT_LINE(V_IDS);
      --根据ID取得用户的名字
      V_USERNAME := GETUSERNAMEBYID(I_ID => V_ID);
    
      IF V_USERNAME = '' THEN
        V_USERNAME := V_ID;
      END IF;
      IF V_USERNAMES IS NULL THEN
        V_USERNAMES := V_USERNAME;
      ELSE
        V_USERNAMES := V_USERNAMES || ';' || V_USERNAME;
      END IF;
    END LOOP;
    DBMS_OUTPUT.PUT_LINE(V_USERNAMES);
    IF SUBSTR(V_USERNAMES, LENGTH(V_USERNAMES)) = ';' THEN
      V_USERNAMES := SUBSTR(V_USERNAMES, 1, LENGTH(V_USERNAMES) - 1);
    END IF;
  EXCEPTION
    WHEN OTHERS THEN
      --V_USERNAMES := I_IDS;
      NULL;
  END;
  --返回
  RETURN V_USERNAMES;
END;

测试:

Trim函数的介绍:

TRIM enables you to trim leading or trailing characters (or both) from a character string. If trim_character or trim_source is a character literal, then you must enclose it in single quotes.

• If you specify LEADING, then Oracle removes any leading characters equal to trim_character.
• If you specify TRAILING, then Oracle removes any trailing characters equal to trim_character.
• If you specify BOTH or none of the three, then Oracle removes leading and trailing characters equal to trim_character.
• If you do not specify trim_character, then the default value is a blank space.
• If you specify only trim_source, then Oracle removes leading and trailing blank spaces.
• The function returns a value with datatype VARCHAR2. The maximum length of the value is the length of trim_source.
• If either trim_source or trim_character is null, then the TRIM function returns null.

Both trim_character and trim_source can be any of the datatypes CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB. The string returned is of VARCHAR2 datatype and is in the same character set as trim_source.

Trim语法:

Oracle TRIM函数的完整语法描述
TRIM([ { { LEADING | TRAILING | BOTH }
      [ trim_character ]
   | trim_character
   }
   FROM
    ]
    trim_source
)

 LEADING | TRAILING | BOTH 三个参数的意义:

首部、尾部、首部和尾部

Examples:

1、默认截取首部和尾部的空格：

 

1 SELECT TRIM(' Hello World ') FROM dual

结果:Hello World

也可以使用：

1 SELECT TRIM(BOTH FROM ' Hello World ') FROM dual

2、Trailing参数的使用；截掉尾部的。

 

1 select trim(trailing  from ' hello world ') from dual

结果: hello world

3、LEADING 参数的使用；截掉首部的。

 

1 select trim(LEADING   from ' hello world ') from dual

结果:hello world 

4、自定义参数的使用：截掉首部和尾部的o

 

1 SELECT TRIM(both 'o' FROM 'ohello worldo') FROM DUAL

结果:hello world

但是他只支持单字符的，不支持多字符:如下：

 

1 SELECT TRIM(both 'ho' FROM 'ohello worldo') FROM DUAL

 

可以使用LTRIM和RTRIM实现相同的功能:

1、LTRIM:实现删除左侧还有oa两个字符中的任意的字符,截止第一个不是它们之中的字符

1  SELECT LTRIM('OaOOOaaaHELLO WORLDO','Oa') FROM DUAL

结果:HELLO WORLDO

RTRIM类似

同时使用解决上面的限制单个字符的问题:

1  select ltrim(rtrim('abHELLO WORLDab','ab'),'ba')  from dual;

a和b的顺序没什么要求

结果:HELLO WORLD

使用RTRIM和LTRIM函数时的注意事项：“ab”不表示整个“ab”字符串进行匹配，而是发现任意的字符“a”或字符“b”均做删除操作。