How to Left Join in Presto SQL? - presto

Question

Can't for the life of me figure out a simple left join in Presto, even after reading the documentation. I'm very familiar with Postgres and tested my query there to make sure there wasn't a glaring error on my part. Please reference code below:
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
Running that gives the following error
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)

Answer 1

The first problem I notice is that your join clause assumes the first sub-query is aliased as a, but it is not aliased at all. I recommend aliasing that table to see if that fixes it (I also recommend aliasing the order_date column explicitly outside of the cast() statement since you are joining on that column).
Try this:
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

Answer 2

One option is to declare your subqueries by using with:
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;