I know a thing or two about SQL Queries, but in this case i can't figure out what to do. So in this case we have a Contact_Salesforce DE where all contacts are in. We have another DE named Placement__c_Salesforce. The relationship between the two is one to many. The Placement DE is where the orders of the contacts are in. I want to make a SQL query which only adds a contact to a new DE when this contact did his first order and NOT get contacts in who already did a few orders.
This is the code as far as i have it:
select contact.id as Id , contact.email as Email , contact.firstname as FirstName from contact_salesforce contact left join placement__c_salesforce placement on placement.candidate__c = contact.id where ?????
Hope someone can help me.