performance tune update sql

Hi All,

Can any one tell me what i am doing wrong here , the following update for millions of records takes hell lot of time.
How can i make this update faster.
Thanks in advance.

Kannan

UPDATE  BR
SET     PPO = ROUND(100 * ST.PPO, 2) ,
        PSO = ROUND(100 * ST.PSO, 2) ,
        KPO = ROUND(100 * ST.KPO, 2) ,
        KSO = ROUND(100 * ST.KSO, 2)
FROM    TABLEA
INNER JOIN ( SELECT ID ,
                    MAX(CASE WHEN COUNTRYID = 1 THEN STRENGTH
                             ELSE 0
                        END) PPO ,
                    MAX(CASE WHEN COUNTRYID = 3 THEN SCOPE
                             ELSE 0
                        END) PSO ,
                    MAX(CASE WHEN COUNTRYID = 4 THEN TOTAL
                             ELSE 0
                        END) KPO ,
                    MAX(CASE WHEN COUNTRYID = 5 THEN VALUE
                             ELSE 0
                        END) KSO
             FROM   TABLEA
             INNER JOIN COUNTRY
                    ON TABLEA.COUNTRYID = COUNTRY.COUNTRYID
                       AND COUNTRYID IN ( 1, 3, 4, 5 )
           ) ST
        ON TABLEA.ID = ST.ID