How to read/write .CSV file into CLOB column in a table of Oracle 10g

Question

I have a requirement which is nothing but a table has two column
create table emp_data (empid number, report clob)
Here REPORT column is CLOB data type which used to load the data from the .csv file.
The requirement here is
1) How to load data from .CSV file into CLOB column along with empid using DBMS_lob utility
2) How to read report columns which should return all the columns present in the .CSV file (dynamically because every csv file may have different number of columns) along with the primariy key empid).
eg: empid report_field1 report_field2
1 x y
Any help would be appreciated.

Answer 1

If I understand you right, you want each row in your table to contain an emp_id and the complete text of a multi-record .csv file.
It's not clear how you relate emp_id to the appropriate file to be read. Is the emp_id stored in the csv file?
To read the file, you can use functions from [UTL_FILE|http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14258/u_file.htm#BABGGEDF] (as long as the file is in a directory accessible to the Oracle server):
declare
    lt_report_clob CLOB;
    l_max_line_length integer := 1024;   -- set as high as the longest line in your file
    l_infile UTL_FILE.file_type;
    l_buffer varchar2(1024);
    l_emp_id report_table.emp_id%type := 123; -- not clear where emp_id comes from
    l_filename varchar2(200) := 'my_file_name.csv';   -- get this from somewhere
begin
   -- open the file; we assume an Oracle directory has already been created
    l_infile := utl_file.fopen('CSV_DIRECTORY', l_filename, 'r', l_max_line_length);
    -- initialise the empty clob
    dbms_lob.createtemporary(lt_report_clob, TRUE, DBMS_LOB.session);
    loop
      begin
         utl_file.get_line(l_infile, l_buffer);
         dbms_lob.append(lt_report_clob, l_buffer);
      exception
         when no_data_found then
             exit;
      end;
    end loop;
    insert into report_table (emp_id, report)
    values (l_emp_id, lt_report_clob);
    -- free the temporary lob
    dbms_lob.freetemporary(lt_report_clob);
   -- close the file
   UTL_FILE.fclose(l_infile);
end;This simple line-by-line approach is easy to understand, and gives you an opportunity (if you want) to take each line in the file and transform it (for example, you could transform it into a nested table, or into XML). However it can be rather slow if there are many records in the csv file - the lob_append operation is not particularly efficient. I was able to improve the efficiency by caching the lines in a VARCHAR2 up to a maximum cache size, and only then appending to the LOB - see [three posts on my blog|http://preferisco.blogspot.com/search/label/lob].
There is at least one other possibility:
- you could use [DBMS_LOB.loadclobfromfile|http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14258/d_lob.htm#i998978]. I've not tried this before myself, but I think the procedure is described [here in the 9i docs|http://download.oracle.com/docs/cd/B10501_01/appdev.920/a96591/adl12bfl.htm#879711]. This is likely to be faster than UTL_FILE (because it is all happening in the underlying DBMS_LOB package, possibly in a native way).
That's all for now. I haven't yet answered your question on how to report data back out of the CLOB. I would like to know how you associate employees with files; what happens if there is > 1 file per employee, etc.
HTH
Regards Nigel
Edited by: nthomas on Mar 2, 2009 11:22 AM - don't forget to fclose the file...