In another post, I saw how to query from the Lead table to the Account table like the following:

select firstname, convertedaccount.lastname from lead where firstname = 'John'

the firstname field is from the Lead table and the lastname field is the Account table.

How can I do the reverse where I want to go from the Account table (knowing the Account.lastname = 'Smith') and pull the firstname field from the Lead table and the lastname field from the Account table.  I don't want to do this with two queries but like above, only use one query.

I can't seem to find any examples where I want to include fields in my query from the Lead table and the related Account table where the ConvertedAccountId matches.  I have tried writing queries but nothing is working.  Isn't this possible?  I can do two queries but I want to only do one and include some fields found in each table.

How can there be records in the Leads table that have the field IsConverted = true but there is no value in ConvertedAccountID, or ConvertedContactID, or ConvertedOpportunityID fields?  I have many records that have this scenario.

I am using the Data Loader to UPSERT Lead records.  I need to have the Data Loader convert the Lead to an Account if the Account record does not already exist.  I cannot find any information in the documentation about how this is done.

I can't seem to find any examples where I want to include fields in my query from the Lead table and the related Account table where the ConvertedAccountId matches.  I have tried writing queries but nothing is working.  Isn't this possible?  I can do two queries but I want to only do one and include some fields found in each table.