SELECT COUNT(*) FROM items
INNER JOIN hosts ON items.hostid=hosts.hostid AND hosts.status IN (0,1)
LEFT OUTER JOIN item_rtdata ON items.itemid=item_rtdata.itemid

-- number of items (all static + discovered) - A
--WHERE items.flags IN (0,4) AND items.status IN (0,1);

-- number of enabled items (supported, on enabled hosts) - E
--WHERE items.flags IN (0,4) AND items.status IN (0) AND hosts.status IN (0) AND item_rtdata.state=0;

-- number of disabled items (or on disabled hosts) - D
--WHERE items.flags IN (0,4) AND (items.status IN (1) OR hosts.status IN (1));

-- number of not supported items (enabled on enabled hosts) - N
--WHERE items.flags IN (0,4) AND items.status IN (0) AND hosts.status IN (0) AND item_rtdata.state=1;

-- A = E + D + N
-- similarly probably for triggers