有关oracle分页返回结果集的问题，高手请进

sunroser

想20条一次向web页面返回结果集，sql中如何限制返回条数，我现在是象酱紫作的，效率很低。。。
SELECT INST_NO,INST_NAME,LEV_SN,ACC_NUM FROM ( SELECT A.INST_NO,A.INST_NAME,C.LEV_NAME LEV_SN,COUNT(*) ACC_NUM,ROW_NUMBER() OVER(ORDER BY A.INST_NO) ROWSEQ FROM T_SYS_INST A,T_CDM_LEDGER B,T_CUST_LEV C WHERE A.INST_LEV = '2' AND SUBSTR(B.FLAG,3,1) = '0' AND B.LEV_SN = C.LEV_SN AND C.LEV_TYPE = '1' AND SUBSTR(A.INST_NO,1,4) = SUBSTR(B.OPEN_INST,1,4) AND A.UPLEV_INST_NO = '370000888' AND B.LEV_SN LIKE '%' GROUP BY A.INST_NO,A.INST_NAME,C.LEV_NAME ) WHERE ROWSEQ BETWEEN 1 AND 5

debuger

用minus函数加rownum