== Parameterized Queries - .NET
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public static bool isUsernameValid(string username) {
	RegEx r = new Regex("^[A-Za-z0-9]{16}$");
	Return r.isMatch(username);
}

// SqlConnection conn is set and opened elsewhere for brevity.
try {
	string selectString = "SELECT * FROM user_table WHERE username = @userID";
	SqlCommand cmd = new SqlCommand( selectString, conn );
	if ( isUsernameValid( uid ) ) {
		cmd.Parameters.Add( "@userID", SqlDbType.VarChar, 16 ).Value = uid;
		SqlDataReader myReader = cmd.ExecuteReader();
		if ( myReader ) {
			// make the user record active in some way.
			myReader.Close();
		}
	} else { // handle invalid input }
}
catch (Exception e) { // Handle all exceptions... }
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