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Oracle LOB Fields

How to compare two clob fields stored in oracle table
1 Solution
Helena Markováprogrammer-analystCommented:
You have to use DBMS_LOB Package.

Subprograms in the DBMS_LOB Package
The more commonly used procedures and functions contained in the DBMS_LOB package can be broadly categorized as follows:  a)  The routines that can modify BLOB, CLOB, and NCLOB values are:
     APPEND()   - append the contents of the source LOB to the destination LOB
     COPY()     - copy all or part of the source LOB to the destination LOB
     ERASE()    - erase all or part of a LOB
     LOADFROMFILE() - load BFILE data into an internal LOB
     TRIM()     - trim the LOB value to the specified shorter length
     WRITE()    - write data to the LOB from a specified offset

b)  The routines that read or examine LOB values are:
      COMPARE()   - comapre two entire or part of two lobs
      GETLENGTH() - get the length of the LOB value
      INSTR()     - return the matching position of the nth occurrence of the pattern in the LOB
      READ()      - read data from the LOB starting at the specified offset
      SUBSTR()    - return part of the LOB value starting at the specified offset

c)  The read-only routines specific to BFILEs are:
      FILECLOSE()   - close the file
      FILECLOSEALL()- close all previously opened files
      FILEEXISTS()  - check if the file exists on the server
      FILEGETNAME() - get the directory alias and file name
      FILEISOPEN()  - check if the file was opened using the input BFILE locators
      FILEOPEN()    - open a file

Here is a procedure published in Note:61737.1 on Metalink:

   dblob BLOB;
   sblob BLOB;
   dclob CLOB;
   sclob CLOB;
   amt   NUMBER;
   dpos  NUMBER;
   spos  NUMBER;
   ret   INTEGER;
   dbms_output.put_line('--------------- COMPARE Begin ---------------');
   dpos := 3;
   spos := 1;
   amt := 5;
    /* test COMPARE for BLOBs */
   SELECT video_clip INTO dblob FROM lob_store WHERE lob_id = 2;
   SELECT video_clip INTO sblob FROM lob_store WHERE lob_id = 4;
   ret := -1;
   ret := dbms_lob.compare(dblob, sblob, amt, dpos, spos);
   dbms_output.put_line('Return value for BLOB: ' || ret);
    /* testing the validity of COMPARE for CLOBs */
   SELECT document INTO dclob FROM lob_store WHERE lob_id = 2;
   SELECT document INTO sclob FROM lob_store WHERE lob_id = 4;
   ret := -1;
   ret := dbms_lob.compare(dclob, sclob, amt, dpos, spos);
   dbms_output.put_line('Return value for CLOB: ' || ret);
    dbms_output.put_line('--------------- COMPARE End   ---------------');
   dbms_output.put_line(' ');
 END tst_compare;

I hope this will help you.

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