Q:

BLOB to String, SQL Server

I have a text string stored as a BLOB data type in a database. I want to extract it by an SQL select query, but I have problems converting/casting from BLOB to readable text.
I've tried e.g.
select convert(nvarchar(40),convert(varbinary(40),BLOBTextToExtract))
from [NavisionSQL$Customer]

I guess I need something similar, but I can't figure out exactly what I need to do the conversion. Can somebody please give me some directions?
Regards

A:

Problem was apparently not the SQL server, but the NAV system that updates the field. There is a compression property that can be used on BLOB fields in NAV, that is not a part of SQL Server. So the custom compression made the data unreadable, though the conversion worked.
The solution was to turn off compression through the Object Designer, Table Designer, Properties for the field (Shift+F4 on the field row). 
After that the extraction of data can be made with e.g.: 
select convert(varchar(max), cast(BLOBFIELD as binary))
from Table
Thanks for all answers that were correct in many ways!

A:

The accepted answer works for me only for the first 30 characters.
This works for me:
select convert(varchar(max), convert(varbinary(max),myBlobColumn)) FROM table_name

A:

It depends on how the data was initially put into the column. Try either of these as one should work:
SELECT CONVERT(NVarChar(40), BLOBTextToExtract)
FROM [NavisionSQL$Customer];

Or if it was just varchar...
SELECT CONVERT(VarChar(40), BLOBTextToExtract)
FROM [NavisionSQL$Customer];

I used this script to verify and test on SQL Server 2K8 R2:
DECLARE @blob VarBinary(MAX) = CONVERT(VarBinary(MAX), 'test');

-- show the binary representation
SELECT @blob;

-- this doesn't work
SELECT CONVERT(NVarChar(100), @blob);

-- but this does
SELECT CONVERT(VarChar(100), @blob);

