I have 2 custom objects in Salesforce.com
One is PersonAccount and one is Accounts.
Within the default "Account" object I have a field called user_id
PersonAccount acts as a junction table to link "Account" to Accounts
PersonAccount does a lookup in Person for user_id Lookup(Account)
How can I build a query to check something in Account to find all the matching items in Accounts?
Currently, Salesforce only permits a single level of nested queries. It cane be done like the following:
[SELECT ID, Name, Field1 from Object__c WHERE Id IN ( SELECT Id FROM Object2__c WHERE Field2 = 'SomeValue')]
However, with the junction object you don't actually need to use a nested query.
Unfortunately, your description isn't clear enough to understand your specific object set-up, so I am going to make some assumptions.
You have three objects, Accounts__c (your custom Accounts Objct), PersonAccount__c (your junction object), and Account (the default Account objects).
The PersonAccount__c object contains two lookup fields (for a true Junction, they should be Master-Detail). The first is to Accounts__c (we will call that lup_cust_accounts__c). The second is to Account (we will call that lup_account__c). [As an aside it is a really bad idea to have an Accounts and Account object. It is going to screw you up because Salesforce will automatically pluralize words and then you will be confused as to which is which.]
Salesforce allows dot relationship lookups in SOQL queries. So if you want to get the ID and Name from custom Accounts Objects when the associated Account object's Name is like "Test", you could do the following:
[SELECT lup_cust_accounts__r.Id, lup_cust_accounts__r.Name FROM PersonAccount__c WHERE lup_account__r.Name LIKE 'Test%'];
Notice the double underscore r instead of double underscore c? That is how you indicate a reference (lookup) rather than the specific field value.
