SELECT   a.co
    ,a.c4
    ,b.c
    ,b.c9
    ,c.c9
    ,b.c4/b.c9*10000
    ,c.c4/c.c9*10000
FROM table_1 a 
RIGHT JOIN 
(SELECT co,MAX(c1) AS c1,c4,c9 FROM table_2 GROUP BY co )b
ON a.co=b.co   
LEFT JOIN table_2 c
ON b.co=c.co AND b.c1>c.c1 AND NOT EXISTS(SELECT 1 FROM table_2 WHERE co=b.co AND c1<b.c1 AND c1>c.c1)
WHERE YEAR(b.c1)=YEAR(20120331000000) AND QUARTER(b.c1)=QUARTER(20120331000000)