目录
1.语法
2. 使用场景
select语句
chaining CTEs 链式
union语句
insert into 语句
create table as 语句
前言
Common Table Expressions（CTE）：公共表达式是一个临时的结果集，该结果集是从with子句中指定的查询派生而来的，紧跟在select 或 insert关键字之前。CTE可以在 select，insert， create table as select 等语句中使用。
1.语法
[wtih CommonTableExpression]
selectcolumn1,column2, ...
from table
[where 条件]
[group by column]
[order by column]
[cluster by column| [distribute by column] [sort by column]
[limit [offset,] rows];2. 使用场景
-
select语句
with tmp as (selectoid,uid,otime,date_format(otime, 'yyyy-MM') as dt,oamount,---计算rk的目的是为了获取记录中的第一条row_number() over (partition by uid,date_format(otime, 'yyyy-MM') order by otime) rkfrom t_order
)selectuid,--每个用户一月份的订单数sum(if(dt = '2018-01', 1, 0)) as m1_count,--每个用户二月份的订单数sum(if(dt = '2018-02', 1, 0)) as m2_count
from tmpgroup by uidhaving m1_count >0 and m2_count=0;-
chaining CTEs 链式
with tmp1 as (selectoid,uid,otime,date_format(otime, 'yyyy-MM') as dt,oamount,---计算rk的目的是为了获取记录中的第一条row_number() over (partition by uid,date_format(otime, 'yyyy-MM') order by otime) as rkfrom t_order
),tmp2 as(selectuid,--每个用户一月份的订单数sum(if(dt = '2018-01', 1, 0)) as m1_count,--每个用户二月份的订单数sum(if(dt = '2018-02', 1, 0)) as m2_countfrom tmp1group by uidhaving m1_count > 0and m2_count = 0)
select * from tmp2 limit 1;
-
union语句
with q1 as (select * from student where num = 95002),q2 as (select * from student where num = 95004)
select * from q1 union all select * from q2;-
insert into 语句
with tmp1 as (selectoid,uid,otime,date_format(otime, 'yyyy-MM') as dt,oamount,---计算rk的目的是为了获取记录中的第一条row_number() over (partition by uid,date_format(otime, 'yyyy-MM') order by otime) as rkfrom t_order
),tmp2 as(selectuid,--每个用户一月份的订单数sum(if(dt = '2018-01', 1, 0)) as m1_count,--每个用户二月份的订单数sum(if(dt = '2018-02', 1, 0)) as m2_countfrom tmp1group by uidhaving m1_count > 0and m2_count = 0)insert into tmp3
select * from tmp2 limit 10;-
create table as 语句
--- 从tmp2 表中取10条数据，基于此创建表tmp3
create table tmp3 as
with tmp1 as (selectoid,uid,otime,date_format(otime, 'yyyy-MM') as dt,oamount,---计算rk的目的是为了获取记录中的第一条row_number() over (partition by uid,date_format(otime, 'yyyy-MM') order by otime) as rkfrom t_order
),tmp2 as(selectuid,--每个用户一月份的订单数sum(if(dt = '2018-01', 1, 0)) as m1_count,--每个用户二月份的订单数sum(if(dt = '2018-02', 1, 0)) as m2_countfrom tmp1group by uidhaving m1_count > 0and m2_count = 0)
select * from tmp2 limit 10;
