从TABLE中选择DISTINCT CLOB_COLUMN;

Question

我想找到可以假设名为COPIA的表中包含的名为CLOB_COLUMN(类型为CLOB)的列的不同CLOB值.

我选择了一个PROCEDURAL方法来解决这个问题,但我更愿意给出一个简单的SELECT,如下所示:SELECT DISTINCT CLOB_COLUMN FROM TABLE避免错误"ORA-00932:不一致的数据类型:预期 - 得到了CLOB"

我怎样才能做到这一点？

提前谢谢您的友好合作.这是我想到的程序方式:

-- Find the distinct CLOB values that can assume the column called CLOB_COLUMN (of type CLOB)
-- contained in the table called COPIA
-- Before the execution of the following PL/SQL script, the CLOB values (including duplicates) 
-- are contained in the source table, called S1
-- At the end of the excecution of the PL/SQL script, the distinct values of the column called CLOB_COLUMN
-- can be find in the target table called S2

BEGIN
   EXECUTE IMMEDIATE 'TRUNCATE TABLE S1 DROP STORAGE';

   EXECUTE IMMEDIATE 'DROP TABLE S1 CASCADE CONSTRAINTS PURGE';
EXCEPTION
   WHEN OTHERS
   THEN
      BEGIN
         NULL;
      END;
END;

BEGIN
   EXECUTE IMMEDIATE 'TRUNCATE TABLE S2 DROP STORAGE';

   EXECUTE IMMEDIATE 'DROP TABLE S2 CASCADE CONSTRAINTS PURGE';
EXCEPTION
   WHEN OTHERS
   THEN
      BEGIN
         NULL;
      END;
END;

CREATE GLOBAL TEMPORARY TABLE S1
ON COMMIT PRESERVE ROWS
AS
   SELECT CLOB_COLUMN FROM COPIA;

CREATE GLOBAL TEMPORARY TABLE S2
ON COMMIT PRESERVE ROWS
AS
   SELECT *
     FROM S1
    WHERE 3 = 9;

BEGIN
   DECLARE
      CONTEGGIO   NUMBER;

      CURSOR C1
      IS
         SELECT CLOB_COLUMN FROM S1;

      C1_REC      C1%ROWTYPE;
   BEGIN
      FOR C1_REC IN C1
      LOOP
         -- How many records, in S2 table, are equal to c1_rec.clob_column?
         SELECT COUNT (*)
           INTO CONTEGGIO
           FROM S2 BETA
          WHERE DBMS_LOB.
                 COMPARE (BETA.CLOB_COLUMN,
                          C1_REC.CLOB_COLUMN) = 0;

         -- If it does not exist, in S2, a record equal to c1_rec.clob_column, 
         -- insert c1_rec.clob_column in the table called S2
         IF CONTEGGIO = 0
         THEN
            BEGIN
               INSERT INTO S2
                    VALUES (C1_REC.CLOB_COLUMN);

               COMMIT;
            END;
         END IF;
      END LOOP;
   END;
END;

Answer 1

您可以比较CLOB的哈希值以确定它们是否不同:

SELECT your_clob
  FROM your_table
 WHERE ROWID IN (SELECT MIN(ROWID) 
                   FROM your_table
                  GROUP BY dbms_crypto.HASH(your_clob, dbms_crypto.HASH_SH1))

编辑:

该HASH功能不保证不会发生冲突.但是,根据设计,你不可能发生任何碰撞.但是,如果碰撞风险(<2 ^ 80？)不可接受,您可以通过比较(具有dbms_lob.compare)具有相同散列的行的子集来改进查询.

Answer 2

使用这种方法。在表配置文件列内容是 NCLOB。我添加了 where 子句以减少运行所需的时间，这是高的，

with
  r as (select rownum i, content from profile where package = 'intl'),
  s as (select distinct (select min(i) from r where dbms_lob.compare(r.content, t.content) = 0) min_i from profile t where t.package = 'intl')
select (select content from r where r.i = s.min_i) content from s
;

它不会因为效率而赢得任何奖品，但应该会奏效。

Answer 3

TO_CHAR在不同的关键字后添加以将 CLOB 转换为 CHAR

SELECT DISTINCT TO_CHAR(CLOB_FIELD) from table1;   //This will return distinct values in CLOB_FIELD

Answer 4

如果可以将字段截断为32767个字符，则可以这样做：

select distinct dbms_lob.substr(FIELD_CLOB,32767) from Table1