Fetch a record from tt_address - typo3

Question

I'm not very familiar with data processing and I'm stuck. I created a new field customer_id in the table tt_content, in which the uid of a tt_address record is stored.
Now I need to read that customer_id from tt_content and fetch the associated record from tt_address to display name and company of it in the fluid template.
tt_content.customerdata =< lib.contentElement
tt_content.customerdata {
templateName = Kundeninfo
dataProcessing {
10 = TYPO3\CMS\Frontend\DataProcessing\DatabaseQueryProcessor
10 {
table = tt_content
uidInList.field = customer_uid
fieldName = customer_uid
???
as = customer
}
}
}
Update:
It woks with
10 = TYPO3\CMS\Frontend\DataProcessing\DatabaseQueryProcessor
10 {
if.isTrue.field = customer_uid
table = tt_content
selectFields = tt_address.*
join = tt_address ON tt_address.uid IN(tt_content.customer_uid)
where = tt_content.uid = 568
as = customer
}
One last problem
In tt_content only one customer_uid (related to the uid of tt_address) is saved for some elements. The above code selects all addresses whose uids are stored in tt_conent. Now i need to get only the matching address to the elements form tt_content. I tested it with one uid of a content element (568) in the code above, that works.
Now i don't know how to code the where condition to read the associated record from tt_address to every content element that has a customer_uid
Thanks