如何以最高性能查询DB2中的数据范围？

Question

通常,我需要从某个范围内的表中检索数据; 例如,每个搜索结果的单独页面.在MySQL中我使用LIMIT关键字但在DB2中我不知道.现在我使用此查询来检索数据范围.

SELECT * 
FROM(
   SELECT  
      SMALLINT(RANK() OVER(ORDER BY NAME DESC)) AS RUNNING_NO
      , DATA_KEY_VALUE
      , SHOW_PRIORITY
   FROM 
      EMPLOYEE
   WHERE 
      NAME LIKE 'DEL%'
   ORDER BY
      NAME DESC
   FETCH FIRST 20 ROWS ONLY
) AS TMP
ORDER BY 
  TMP.RUNNING_NO ASC
FETCH FIRST 10 ROWS ONLY

但我知道这是不好的风格.那么,如何查询最高性能？

Answer 1

我的要求已经添加到DB2 9.7.2中.

DB2 9.7.2为限制查询结果添加了新语法,如下所示:

SELECT * FROM TABLE LIMIT 5 OFFSET 20

数据库将从行号中检索结果.21 - 25

Answer 2

这很困难，这取决于你有哪个数据库。

例如：

SELECT * FROM ( 
    SELECT 
      ROW_NUMBER() OVER (ORDER BY ID_USER ASC) AS ROWNUM,  
      ID_EMPLOYEE, FIRSTNAME, LASTNAME 
    FROM EMPLOYEE 
    WHERE FIRSTNAME LIKE 'DEL%' 
  )  AS A WHERE A.rownum
BETWEEN 1 AND 25