How many Eredivisie teams have played in 2008?
Eredivisie is the name of division; 2008 refers to season; teams refer to HomeTeam;
SELECT COUNT(DISTINCT T1.HomeTeam) FROM matchs AS T1 INNER JOIN divisions AS T2 ON T1.Div = T2.division WHERE T2.name = 'Eredivisie' AND T1.season = 2008