From: Warren Young
Date: October 12 2007 6:22am
Subject: Re: varchar field > 65K
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John Gehring wrote:
> I am adding records to my MySQL database that contains a column of type
> 'mediumtext' (call it ColA). The amount of data is roughly 75K bytes. If I
> use the SELECT ... INTO OUTFILE ... statement to get the data, I
> successfully get all the data of the record. However, if I use a select
> statement within an embedded application (using mysql++), the data from ColA
> is truncated at 65K bytes.

Things to check:

- What character set are you using?  Unicode character representations 
may do surprising things when processed by naive code.  See chapter 6 in 
the user manual.

- "65K" bothers me.  Are you using SI suffixes here -- 65,000 bytes -- 
or do you mean that it's actually getting over the special 64K boundary?

- Are you sure you don't need a BLOB column here?  Or, at least treating 
it with the precautions due a BLOB column?  See examples/load_jpeg.cpp 
and examples/cgi_jpeg.cpp.

> I see quite a bit of documentation for the mysql
> embedded library related to binding data for result sets. But I don't see
> anyplace in the mysql++ code that uses that functionality (like
> mysql_stmt_bind_result()).

Yes, but there's no requirement to use those APIs.  MySQL++ takes the 
traditional approach: it uses text representations of data, in plain old 
SQL forms.  You must use BLOBs to get bit-for-bit accuracy, and even 
then, it goes across the wire in escaped text form.

> Am I missing something, or does the mysql++
> library have a limit on how large a field of data can be returned from a
> select statement?

MySQL++ imposes no limits above what the underlying C API does.  That's 
not to say that you can't abuse the library to make it truncate data, 
just that there are proper ways to get the data without truncation.