Sucrose is a covalent compound. Whether a compound is ionic or covalent depends on the relative attraction the compound's atoms have for electrons. Sucrose is composed of carbon, hydrogen and oxygen, all of which have similar enough attractions for electrons to form covalent bonds with each other.
A covalent bond is a bond where electrons are shared between the atoms of a compound. Ionic bonds, such as the bonds in table salt, are made when one atom completely takes the electrons from the other. When sugar dissolves in water, the sucrose molecules remain whole, but when salt dissolves, it dissociates into individual sodium and chloride ions.