Probably, it's that your code is liable to SQL injection, and that affects what you have actually saved.
The code you show probably isn't vulnerable to SQL Injection because I suspect that
m_id
is not a string - but it's indicative that the rest of your code is.
Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.
When you concatenate strings, you cause problems because SQL receives commands like:
SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'
The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;
Which SQL sees as three separate commands:
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
DROP TABLE MyTable;
A perfectly valid "delete the table" command
And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.
So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?
And that has another effect: it wrecks your data when you try to save it, you don;t know that it;''s happened, and you get a "Parameter is not valid" error when you try to regenerate your images. See here:
Why do I get a "Parameter is not valid." exception when I read an image from my database?[
^]