How do I use a table name that's returned in a select statement, in a join? - sql

Question

*Note: This is not the same as the "possible duplicate". Here, the table name will be different for each record returned in the SELECT statement. So I can't just "set" a variable like set #tableName = 'whatever'.
Here's my SQL - take a look at my last inner join. e.Name from the table EmailSendDefintion is the name of the table I need to join to. So, this is kind of dynamic, I know, but how do I join to a table that is stored in a field in another table?
select top 5000
x.HL_ACCT_ID as 'HL_ACCT_ID',
x.SALE_CODE as 'SALE_CODE',
s.SubscriberKey as 'EmailAddress',
o.EventDate as 'Opened',
c.EventDate as 'Clicked',
b.EventDate as 'Bounced'
from c100._sent s with (nolock)
inner join c100._job j with (nolock) on s.jobid = j.jobid
inner join emailsenddefinition e with (nolock) on e.customerkey = j.emailsenddefinition
left join c100._open o with (nolock) on o.jobid = s.jobid and o.subscriberkey = s.subscriberkey
left join c100._click c with (nolock) on c.jobid = s.jobid and c.subscriberkey = s.subscriberkey
left join c100._bounce b with (nolock) on b.jobid = s.jobid and b.subscriberkey = s.subscriberkey
inner join c100.[e.name] x with (nolock) on x.EmailAddress = s.SubscriberKey
where e.clientid = 100

Answer 1

Perhaps you could just create a view that outputs the union of all the e.name tables? Then join to the view.
In order to keep this short, let's say you have just 2 different tables whose name could be in the e.name column, SubscriberEmail1 and SubscriberEmail2.
Then you could create a view like this:
CREATE VIEW SubscriberEmailUnion
AS
SELECT
'SubscriberEmail1' as TableName,
HL_ACCT_ID,
SALE_CODE,
EmailAddress
FROM SubscriberEmail1
UNION
SELECT
'SubscriberEmail2' as TableName,
HL_ACCT_ID,
SALE_CODE,
EmailAddress
FROM SubscriberEmail2
GO
Note that each part of the view is adding the name of it's underlying table as a column. You can then change your final join to:
inner join SubscriberEmailUnion x with (nolock) on (
x.EmailAddress = s.SubscriberKey
AND x.TableName = e.Name
)
I'm personally most familiar with MS Sql Server so my sample uses that syntax. Should be easy enough to change to work with a different server if necessary though.
For performance you can then use whatever feature your DB has, indexed views etc.

Answer 2

How many tables do you have? If not too many one option would be to left join all of them
left join c100.table1 x1 on x1.EmailAddress = s.SubscriberKey and [e.name] = 'table1'
left join c100.table2 x1 on x2.EmailAddress = s.SubscriberKey and [e.name] = 'table2'
etc...
and then in the select
coalesce(x1.HL_ACCT_ID, x2.HL_ACCT_ID, etc...) as 'HL_ACCT_ID',