Two major problems with that:
1) 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. Use Parametrized 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?
Think about what you are doing! You pass the username as a parameter, so why the heck are you tacking it on at the end and making your code vulnerable as well?
2) Never store passwords in clear text - it is a major security risk. There is some information on how to do it here:
Password Storage: How to do it.[
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To give you an idea how we feel about that kind of thing, see here:
Code Crime 1[
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Then we come to minor problems: why are you setting the username, when you know it's the same value already? Because if it was different, it wouldn't match any rows!
And finally: why is it changing the name field? Because you told it to...
If you want the name to remain untouched when it is blank, you need to check in your C# code, and either use a different query, or pass the current value instead. If you tell SQL "set it to this" then that is exactly what it will do...