Sugars can exists as either configurational isomers (interconverted only by breaking covalent bonds) and conformational isomers. The figure below reviews different types of isomers.
The configurational isomers include enantiomers (stereoisomers that are mirror images of each other), diastereomers (stereoisomers that are not mirror images), epimers (diastereomers that differ at one stereocenter), and anomers (a special form of stereoisomer, diastereomer, and epimer that differ only in the configuration around the carbon which was attacked in the intramolecular nucleophilic attack to produces the a and b isomers).
Sugars can also exist as conformational isomers, which interchange without breaking covalent bonds. These include chair and boat conformations of the cyclic sugars.