New to SQL writing a query with nesting and joins - sql

Question

Here is my query I am not sure why it wont run. it doesnt seem to like the joins. It ran without the nesting but now the now the joins wont work.
select *
from (
select * ,
row_number () over (partition by t.activity_type__c order by t.ActivityDate desc) ,
x.name,
MAX(t.ActivityDate) as Last_Activity_Date,
/* all these below x or a alias? */
x.Channel__c,
x.Account_18_Digit_ID__c,
x.Advisor_Approach__c,
x.name,
x.BillingState,
x.Current_Month_WT_AUM__c,
x.WT_ETF_AUM_mil__c,
x.ETF_AUM__c,
x.WT_ETF_Market_Share__c,
x.priority_type__C,
x.phone,
/* x.ownerid,
x.ID ? */
rn
from account a
) where rn=1
join [User] u on u.id = x.OwnerId
left join Task t on t.WhatId = x.Id
where t.Activity_Type__c <> 'attempt' and
( Advisor_Approach__c like 'CAPFINANCIAL_SECURITIES%' )

Answer 1

There's a lot going on here, so to start out we need to format it with better indentation. This helps make it obvious we have two where clauses at the same nesting level, one of which is out of place (before the JOINs).
Looking deeper, I see a MAX() function, but it's not allowed in this context unless you also have a GROUP BY clause. We're also missing an alias for the inner query... perhaps this is where the x is supposed to come from? And the inner nested query references columns from tables in the outer query, which are not yet available. Also, you can't use a windowing function result at the same level of nesting, and I don't see what the User table is needed for. After we fix most of this, we also no longer need to nest the accounts table by itself.
This is closest I could come to fixing all these issues, but I know it's still wrong because of (at least) the MAX() function:
select *
from (
select a.name,
/* MAX(t.ActivityDate) as Last_Activity_Date, */
a.Channel__c,
a.Account_18_Digit_ID__c,
a.Advisor_Approach__c,
a.name,
a.BillingState,
a.Current_Month_WT_AUM__c,
a.WT_ETF_AUM_mil__c,
a.ETF_AUM__c,
a.WT_ETF_Market_Share__c,
a.priority_type__C,
a.phone,
/* a.ownerid, a.ID ? */
row_number () over (partition by t.activity_type__c order by t.ActivityDate desc) as rn
from account a
join [User] u on u.id = a.OwnerId
left join Task t on t.WhatId = a.Id
where t.Activity_Type__c <> 'attempt'
and ( Advisor_Approach__c like 'CAPFINANCIAL_SECURITIES%' )
) x
where rn = 1

Answer 2

It seems you have the query upside-down. You seem to be trying to join the lastest task per activity type to the account, but instead of selecting from account and then joining the latest tasks, you are trying to select the lastest task from the account table somehow, which cannot work of course.
Something along the lines of:
select *
from account a
join [User] u on u.id = a.ownerid
left join
(
select
task.*,
row_number() over (partition by activity_type__c order by activitydate desc) as rn
from task
where activity_type__c <> 'attempt'
) t on t.whatid = a.id and t.rn = 1
where a.advisor_approach__c like 'CAPFINANCIAL_SECURITIES%'
order by a.id, t.activity_type__c;