Not like that! 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?
In addition, you should never hard code connections strings - always store these in a config file so that you don't have to change them every time you release a new version! And storing them in every method? That's just insane - and a recipe for major problems when you try to fix a bug and find you are working to production DB in a method that deletes the whole DB by accident...
Read it from your config file once, and reuse the string from there.
Then look at fixing the problem you have noticed: take the comma away after "StudentID" in your INSERT command:
string query = "INSERT INTO Voting (StudentID) VALUES ( ... )";