c# webclient select sql string

c# webclient select sql string

I'm using a WebClient to read an write an remote db. I'm trying to use
this query to write in a table but it doesn't work:
string query "INSERT INTO ProgettoGruppi (`id`, `progettoID`, `gruppoID`,
`orePreviste`, `oreAttuali`, `stato`) VALUES (NULL, 1, 2, 0, 0, 'test3')"
If I replace 'test3' with NULL it work fine.
wich is the correct format to write 'test3' in the string?