Oracle安装程序 ：

CREATE TABLE your_table ( your_list_column ) AS
  SELECT 'a,a,b,c,d' FROM DUAL UNION ALL -- duplicates both at head
  SELECT 'a,b,a,c,d' FROM DUAL UNION ALL -- duplicates at head and middle
  SELECT 'a,b,c,d,a' FROM DUAL UNION ALL -- duplicates at head and tail
  SELECT 'a,b,b,c,d' FROM DUAL UNION ALL -- duplicates at middle and next item
  SELECT 'a,b,c,b,d' FROM DUAL UNION ALL -- duplicates at middle and middle
  SELECT 'a,b,c,d,b' FROM DUAL UNION ALL -- duplicates at middle and tail
  SELECT 'a,b,c,d,d' FROM DUAL UNION ALL -- duplicates both at tail
  SELECT 'a,b,a,c,b' FROM DUAL UNION ALL -- two pairs of duplicates
  SELECT 'a,b,c,d,e' FROM DUAL;          -- no duplicates

要获取具有重复值的列表，可以在正则表达式中使用向后引用：

SELECT *
FROM   your_table
WHERE  REGEXP_LIKE( ',' || your_list_column || ',', ',([^,]+),(.+,)?\1,' )

输出 ：

YOUR_LIST_COLUMN
----------------
a,a,b,c,d
a,b,a,c,d
a,b,c,d,a
a,b,b,c,d
a,b,c,b,d
a,b,c,d,b
a,b,c,d,d
a,b,a,c,b

要获取第一个重复值，您可以提取上述正则表达式的第一个子组：

SELECT your_list_column,
       REGEXP_SUBSTR( ',' || your_list_column || ',', ',([^,]+),(.+,)?\1,', 1, 1, NULL, 1 )
         AS duplicate_value
FROM   your_table
WHERE  REGEXP_LIKE( ',' || your_list_column || ',', ',([^,]+),(.+,)?\1,' )

输出 ：

YOUR_LIST_COLUMN DUPLICATE VALUE
---------------- ---------------
a,a,b,c,d        a
a,b,a,c,d        a
a,b,c,d,a        a
a,b,b,c,d        b
a,b,c,b,d        b
a,b,c,d,b        b
a,b,c,d,d        d
a,b,a,c,b        a

然后，要获取唯一值，请使用split_string()此处定义的函数（但使用用户定义的类型而不是预定义的类型VARRAY）：

CREATE OR REPLACE TYPE stringlist IS TABLE OF VARCHAR2(4000);
/

CREATE OR REPLACE FUNCTION split_String(
  i_str    IN  VARCHAR2,
  i_delim  IN  VARCHAR2 DEFAULT ','
) RETURN stringlist DETERMINISTIC
AS
  p_result       stringlist := stringlist();
  p_start        NUMBER(5) := 1;
  p_end          NUMBER(5);
  c_len CONSTANT NUMBER(5) := LENGTH( i_str );
  c_ld  CONSTANT NUMBER(5) := LENGTH( i_delim );
BEGIN
  IF c_len > 0 THEN
    p_end := INSTR( i_str, i_delim, p_start );
    WHILE p_end > 0 LOOP
      p_result.EXTEND;
      p_result( p_result.COUNT ) := SUBSTR( i_str, p_start, p_end - p_start );
      p_start := p_end + c_ld;
      p_end := INSTR( i_str, i_delim, p_start );
    END LOOP;
    IF p_start <= c_len + 1 THEN
      p_result.EXTEND;
      p_result( p_result.COUNT ) := SUBSTR( i_str, p_start, c_len - p_start + 1 );
    END IF;
  END IF;
  RETURN p_result;
END;
/

然后，您可以将其与SET()收集功能结合使用：

SELECT t.*,
       (
         SELECT LISTAGG( COLUMN_VALUE, ',' ) WITHIN GROUP ( ORDER BY ROWNUM )
         FROM   TABLE( SET( split_string( t.your_list_column ) ) )
       ) AS unique_list
FROM   your_table t

输出 ：

YOUR_LIST_COLUMN UNIQUE_LIST
---------------- ---------------
a,a,b,c,d        a,b,c,d
a,b,a,c,d        a,b,c,d
a,b,c,d,a        a,b,c,d
a,b,b,c,d        a,b,c,d
a,b,c,b,d        a,b,c,d
a,b,c,d,b        a,b,c,d
a,b,c,d,d        a,b,c,d
a,b,a,c,b        a,b,c
a,b,c,d,e        a,b,c,d,e