I have these queries,
select ownerId from account
select firstname from user
How can I join them? OR How can I get the owner name from account table? Thanks in advance.
SELECT Owner.Name FROM Account WHERE ...
Any time you've got a standard field which is a lookup, you can just remove 'Id' from the end and add '.Name' (or whatever other field you want). If you're dealing with a custom field (ending in __c), you can do the same with '__r.Name'
select owner.name from Account where ...