如何在 Presto SQL 中左连接？答案

【问题标题】：How to Left Join in Presto SQL?如何在 Presto SQL 中左连接？
【发布时间】：2018-07-20 10:10:03
【问题描述】：

即使在阅读文档之后，我也无法在 Presto 中找到一个简单的左连接。我对 Postgres 非常熟悉，并在那里测试了我的查询，以确保我没有明显的错误。请参考以下代码：

select * from

(select cast(order_date as date),   
        count(distinct(source_order_id)) as prim_orders, 
        sum(quantity) as prim_tickets, 
        sum(sale_amount) as prim_revenue 
from table_a
where order_date >= date '2018-01-01'
group by 1)

left join

(select summary_date, 
        sum(impressions) as sem_impressions, 
        sum(clicks) as sem_clicks, 
        sum(spend) as sem_spend,  
        sum(total_orders) as sem_orders, 
        sum(total_tickets) as sem_tickets, 
        sum(total_revenue) as sem_revenue 
from table_b
where site like '%SEM%'
and summary_date >= date '2018-01-01'
group by 1) as b

on a.order_date = b.summary_date

运行时出现以下错误

SQL Error: Failed to run query
  Failed to run query
    line 1:1: mismatched input 'on' expecting {'(', 'SELECT', 'DESC', 'WITH', 
'VALUES', 'CREATE', 'TABLE', 'INSERT', 'DELETE', 'DESCRIBE', 'GRANT', 
'REVOKE', 'EXPLAIN', 'SHOW', 'USE', 'DROP', 'ALTER', 'SET', 'RESET', 'START', 'COMMIT', 'ROLLBACK', 'CALL', 'PREPARE', 'DEALLOCATE', 'EXECUTE'} (Service: AmazonAthena; Status Code: 400; Error Code: InvalidRequestException; Request ID: a33a6671-07a2-4d7b-bb75-f70f7b82409e)
line 1:1: mismatched input 'on' expecting {'(', 'SELECT', 'DESC', 'WITH', 'VALUES', 'CREATE', 'TABLE', 'INSERT', 'DELETE', 'DESCRIBE', 'GRANT', 'REVOKE', 'EXPLAIN', 'SHOW', 'USE', 'DROP', 'ALTER', 'SET', 'RESET', 'START', 'COMMIT', 'ROLLBACK', 'CALL', 'PREPARE', 'DEALLOCATE', 'EXECUTE'} (Service: AmazonAthena; Status Code: 400; Error Code: InvalidRequestException; Request ID: a33a6671-07a2-4d7b-bb75-f70f7b82409e)

【问题讨论】：

标签： presto

【解决方案1】：

我注意到的第一个问题是您的连接子句假定第一个子查询别名为a，但它根本没有别名。我建议为该表设置别名以查看是否可以修复它（我还建议在 cast() 语句之外显式地为 order_date 列添加别名，因为您正在加入该列）。

试试这个：

select * from

(select cast(order_date as date) as order_date,   
        count(distinct(source_order_id)) as prim_orders, 
        sum(quantity) as prim_tickets, 
        sum(sale_amount) as prim_revenue 
from table_a
where order_date >= date '2018-01-01'
group by 1) as a

left join

(select summary_date, 
        sum(impressions) as sem_impressions, 
        sum(clicks) as sem_clicks, 
        sum(spend) as sem_spend,  
        sum(total_orders) as sem_orders, 
        sum(total_tickets) as sem_tickets, 
        sum(total_revenue) as sem_revenue 
from table_b
where site like '%SEM%'
and summary_date >= date '2018-01-01'
group by 1) as b

on a.order_date = b.summary_date

【讨论】：

【解决方案2】：

一种选择是使用with 声明您的子查询：

with a as 
  (select cast(order_date as date),   
    count(distinct(source_order_id)) as prim_orders, 
    sum(quantity) as prim_tickets, 
    sum(sale_amount) as prim_revenue 
  from table_a
  where order_date >= date '2018-01-01'
  group by 1),

b as 
  (select summary_date, 
    sum(impressions) as sem_impressions, 
    sum(clicks) as sem_clicks, 
    sum(spend) as sem_spend,  
    sum(total_orders) as sem_orders, 
    sum(total_tickets) as sem_tickets, 
    sum(total_revenue) as sem_revenue 
  from table_b
  where site like '%SEM%'
  and summary_date >= date '2018-01-01'
  group by 1)

select * from a
left join b
on a.order_date = b.summary_date;

【讨论】：