WITH

WITH子句定义查询子句的命名关系，可以展平嵌套查询或简化子查询语句。

例如下面的查询语句是等价的：

SELECT name, maxprice FROM (SELECT name, MAX(price) AS maxprice FROM fruit GROUP BY name) AS x;

WITH x AS (SELECT name, MAX(price) AS maxprice FROM fruit GROUP BY name) SELECT name, maxprice FROM x;

多个子查询：

with 
t1 as(select name,max(price) as maxprice from fruit group by name),
t2 as(select name,avg(price) as avgprice from fruit group by name)
select t1.*,t2.* from t1 join t2 on t1.name = t2.name;

WITH的链式形式：

WITH
x AS (SELECT a FROM t),
y AS (SELECT a AS b FROM x),
z AS (SELECT b AS c FROM y)
SELECT c FROM z;