优化这个oracle sql语句: select O_CODE,O_NAME,FIN_PROD_CUSTOMER_FLAG from (SELECT A.O_CODE, A.O_NAME,a.FIN_PROD_CUSTOMER_FLAG FROM TCORP A WHERE ('' is NULL OR FIN_PROD_CUSTOMER_FLAG = '') AND ((1 = 1 AND (INSTR(O_CODE, 'w') > 0 OR INSTR(Q_CODE, 'w') > 0 OR INSTR(PYM_CODE, 'w') > 0) ) OR INSTR(O_NAME, 'w') > 0 OR INSTR(O_SNAME, 'w') > 0) order by length(O_NAME) ) where rownum <= 15

这个 SQL 查询语句可以进行以下优化：

1. 使用绑定变量代替空字符串

将查询条件中的空字符串 '' 改为绑定变量，这样 Oracle 可以重用执行计划，提高查询性能。例如：

SELECT A.O_CODE, A.O_NAME,a.FIN_PROD_CUSTOMER_FLAG 
FROM TCORP A 
WHERE (:flag IS NULL OR FIN_PROD_CUSTOMER_FLAG = :flag) 
AND (
  (1 = 1 AND (
    INSTR(O_CODE, :search) > 0 OR 
    INSTR(Q_CODE, :search) > 0 OR 
    INSTR(PYM_CODE, :search) > 0
  )) OR 
  INSTR(O_NAME, :search) > 0 OR 
  INSTR(O_SNAME, :search) > 0
) 
ORDER BY LENGTH(O_NAME) 
FETCH FIRST 15 ROWS ONLY;

2. 使用索引

在这个查询中，可以为 FIN_PROD_CUSTOMER_FLAG、O_CODE、Q_CODE、PYM_CODE、O_NAME 和 O_SNAME 列分别创建索引，以加速查询。例如：

CREATE INDEX idx_fpcf ON TCORP (FIN_PROD_CUSTOMER_FLAG);
CREATE INDEX idx_oc ON TCORP (O_CODE);
CREATE INDEX idx_qc ON TCORP (Q_CODE);
CREATE INDEX idx_pymc ON TCORP (PYM_CODE);
CREATE INDEX idx_oname ON TCORP (O_NAME);
CREATE INDEX idx_osname ON TCORP (O_SNAME);

3. 使用 UNION ALL

将查询条件中的 OR 连接的子查询，拆分成多个 SELECT 语句，然后使用 UNION ALL 连接它们，这样 Oracle 可以并行执行这些子查询，提高查询性能。例如：

SELECT A.O_CODE, A.O_NAME,a.FIN_PROD_CUSTOMER_FLAG 
FROM TCORP A 
WHERE (:flag IS NULL OR FIN_PROD_CUSTOMER_FLAG = :flag) 
AND INSTR(O_NAME, :search) > 0 
UNION ALL 
SELECT A.O_CODE, A.O_NAME,a.FIN_PROD_CUSTOMER_FLAG 
FROM TCORP A 
WHERE (:flag IS NULL OR FIN_PROD_CUSTOMER_FLAG = :flag) 
AND INSTR(O_SNAME, :search) > 0 
UNION ALL 
SELECT A.O_CODE, A.O_NAME,a.FIN_PROD_CUSTOMER_FLAG 
FROM TCORP A 
WHERE (:flag IS NULL OR FIN_PROD_CUSTOMER_FLAG = :flag) 
AND (
  INSTR(O_CODE, :search) > 0 OR 
  INSTR(Q_CODE, :search) > 0 OR 
  INSTR(PYM_CODE, :search) > 0
) 
ORDER BY LENGTH(O_NAME) 
FETCH FIRST 15 ROWS ONLY;

综上所述，可以通过使用绑定变量、索引、UNION ALL 等方法来优化这个 SQL 查询语句的性能。