pl/sql 求助！！语句优化

SELECT B.BH AAC001,B.DWYJ,B.GRYJ,ROUND(B.JFJS/12,2) BAC121,
                     SUBSTR(TO_CHAR(DECODE(ROUND(MONTHS_BETWEEN(TO_DATE(SUBSTR(TRIM(REPLACE(NVL(ZZRQ,'19000101'),'.','')),1,6)||'01','YYYYMMDD'),
                            TO_DATE(SUBSTR(TRIM(REPLACE(NVL(QSRQ,'19000101'),'.','')),1,6)||'01','YYYYMMDD')))+1,
                            '1',TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),
                            '2',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),1),
                            '3',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '4',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '5',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '6',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '7',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '8',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '9',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '10',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '11',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2),
                            '12',ADD_MONTHS(TO_DATE(TRIM(REPLACE(QSRQ,'.','')),'YYYYMMDD'),2)),'YYYYMMDD'),1,6) AAE002,
                     B.DWDM AAB001
                FROM HRB_JG_OLD.CB307 B
               WHERE B.BH='20008526'
                 AND GRYJ<>0
                 AND FLAG='1'
               UNION