So, I don’t think that there is a difference between the 2nd and 3rd (believe me if I am wrong!), However I am sure of the difference between the 1st and 2nd
indexes used to indicate the field - on the Thinking Sphinx website:
Fields are the content for your searches - so if you want words to be attached to a specific document, you need to make sure theyre in the field of your index. They are just string data - you can have numbers and dates, etc. In your fields, but Sphinx will only consider them as strings, and nothing more.
has used to indicate an attribute - again, according to the Thinking Sphinx website:
, . Sphinx , theyre : , , datetimes ( Unix - , , ), . , , , .