HELP! Database query issue!

Hi Experts,

We are implementing a complicated employee search solution in the biggest human resource system on earth. And now there is a serious database query performance issue. It takes more than 300 seconds to excute the following SQL statement at the first query, and about 2.5 seconds after the first query using the same conditions.

SELECT PERNR INTO TABLE T_RESULT FROM PA0001

WHERE WERKS IN P1

AND ZZ_POSLV = '08'.

There are about 10,000,000 records in table PA0001, 150,0000 records fit the first condition, and 200 records fit both conditions.

Table PA0001 is SAP buffer disabled, and field ZZ_POSLV is customer field without database index.

What's the difference between the first query and the second? How can we improve the performace of the first time query? The performance of the second is acceptable.

Best Regards,

Guo Guo Qing