Previous Topic

Next Topic

Book Contents

Book Index

Displaying BLOBs and CLOBs

Dealing with LOBs

BLOB and CLOB columns are difficult to display because:

BLOBs and CLOBs are known generically as LOBs.

In addition, BLOBs and CLOBs often need to be sent to an external application to be displayed. For instance, an image file held in a BLOB column will need to be displayed using an image-viewer such as MS Paint. A Word document will need to be sent to MS Word.

Setting LOB options

To deal with these requirements, AQT has an option to export a LOB column to a file. Select this option by Options > Display Options > How to Display Lobs. Select Send to Files.

You can also select what column-types this is done for: BLOBs, CLOBs and LONG VARCHAR. To explain what these types mean:

When you use this option:

Storing and clearing LOBs

Problem when running multiple AQT Sessions

If you are running multiple AQT sessions, then it is possible for these sessions to interfere with each others LOB files. This is because both these sessions will use the same LOB directory and it could happen that they use the same LOB file names.

This issue is more of a problem in batch AQT as some functions (such as Data Compare) can retain the LOB files for the duration of the batch session.

To avoid such issues, you can manually set the directory used for LOBs. This is done with the following AQT scripting command:

--aqt options,lobdir="c:\aqt\workfiles\lobs"

Performance issues with LOBs

Unicode

If you have enabled Unicode, AQT will write all CLOBs and Long Varchars values as unicode files. If you don't want your files in this format, you should disable Unicode (see Options > Unicode Options).

Limitations and issues with LOBs

The Row Detail window does not (yet) display LOB values. In a future release we may amend this to display the LOB files, plus edit and create LOBs (by linking to the appropriate external application).

Oracle ODBC driver needed

Displaying LOBs with Sybase

In order to display Sybase LOBs, you need to have a high value set for your TEXTSIZE setting. This can be done with (for example):

set textsize 20971520

Alternatively, you can change the Default Buffer Size for Long Columns setting on the configuration of the ODBC Datasource.