!!!DB2 CASE式とNULL
[DB2][Database]{{category SQL}}
,CASE 式,同等の式
,CASE WHEN e1=e2 THEN NULL ELSE e1 END,NULLIF(e1，e2)
,CASE WHEN e1 IS NOT NULL THEN e1 ELSE e2 END,COALESCE(e1，e2)
,CASE WHEN e1 IS NOT NULL THEN e1 ELSE COALESCE(e2，...，eN) END,COALESCE(e1，e2，...，eN)