oracle while的用法示例分享

三叶草

当查询中多次用到某一部分时，可以用Oracle with语句创建一个公共临时表。因为子查询在内存临时表中，避免了重复解析，所以执行效率会提高不少。临时表在一次查询结束自动清除。
一般语法格式：

with   
alias_name1 as  (subquery1),  
alias_name2 as  (subQuery2),  
……  alias_nameN as  (subQueryN)  
select col1,col2…… col3
from alias_name1,alias_name2……,alias_nameN

Oracle with语句的例子：

WITH  Q1 AS (SELECT 3 + 5 S FROM DUAL), 
Q2 AS (SELECT 3 * 5 M FROM DUAL), 
Q3 AS (SELECT S, M, S + M, S * M FROM Q1, Q2)  
SELECT * FROM Q3;

输出结果：

1 8 15 23 120