With查詢語句已with開頭，相當於在查詢之前先構建一個臨時表，被指定的查詢結果存與臨時表中，之後便可多次使用它做進一步的分析和處理。
語法：
with _tempTable as (select * from table ) select * from _tempTable
例子：
with _tempStudent as( select * from t_student t where class = '初二3班' ) select sex,count(1) nums from _tempStudent where sex = '男' and height > '170' union all select sex,count(1) nums from _tempStudent where sex = '女' and height > '160'
多個with as 用法 每個臨時存量直接用 "," 隔開
with t1 as (
select * from student where name in('張三','李四')
),t2 as (
select * from student where name in('王五')
)
select * from t1
union
select * from t2如果with as 有嵌套的情況， 多個with as，後面的as內部可以直接調用先聲明的臨時對象
with t1 as (
select * from student where name in('張三','李四')
),t2 as (
select * from t1 where name in('王五')
)
select * from t2