Accessing IMAGE Columns in SQL Server

Question

I'm trying to use the TG4MSSQL to access tables in a SS2k database. All is well, except for 1 table that has an IMAGE column in it. I must say that I'm a little surprised and disappointed that the 10gR2 gateway for MSSQL apparently translates these things into LONG RAW columns, which are known to be antiquated and minimally supported. However, I still need access to the data, and ultimately, I need it in a BLOB. Doing simple queries (in TOAD) such as:
select * from image@tg4ss where image_id = 1;
returns the row, and I can use TOAD to determine that all the data is there. However, apparently, you cannot use PL/SQL to bind more than 32K of this data into a variable, so I haven't had much success there.
The only way I know of converting a long raw to a blob is to use the to_lob function, but that's only good in the select list of a subquery of an insert statement. Thing is, that doesn't seem to work with the gateway. I tried something like:
insert into my_blob_table( id, image )
select id, to_lob(image) as image from image@tg4ss where id = 1;
That gets me a ORA-00997: illegal use of LONG datatype.
In fact, I can't even do this:
insert into my_long_raw_table( id, image )
select id, image from image@tg4ss where id = 1;
I get the same error on that command.
Now, I can do this, but I only get the first 32k of the image:
begin
for I in (select id, image from IMAGE@tg4ss)
loop
insert into my_long_raw_table( id, image )
values (I.id, I.image);
end loop;
end;
So, does anyone know how you can get image data out of an SQL Server database into a blob value? If so, I'd appreciate a reply. Thanks.
-Rich.

Answer 1

Hello Rich,
I found your article after running into the same problem. I imagine you've dealt with this one way or another already but just in case...
The reason the LONG RAW gets truncated is explained in:
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14261/datatypes.htm#i43252
Basically, LONG RAW variables are limited to 32760 bytes inside PL/SQL. The ORA-00997 error is explained a little in:
http://www.dbaxchange.com/3_4_longdatatypes.htm
The only solution I found to work was to create a Java utility that read in each LONG RAW value (one at a time) and then update a record in a table's BLOB column. This was even a bit tricky. I found the gateway would lock up if I tried to do too much at a time. I kept it simple my reading all column IDs into an array and then looping through the array while executing a simple select statement that retrieved the LONG RAW value. I concatenated the id to the end of the select statement because prepared statements seemed to be one of the reasons the gateway locked up. I used a ByteArrayInputStream object to populate the BLOB in an update prepared statement for each LONG RAW value processed in the loop.
- Aaron