Can we put conditions in Composite Request Body

I want to create a Composite Request Body. 

My requirement is, 

I have to query some record in the 1st subRequest, by taking some field value from Lead Object. 

If the record exists with that field value, then in the second subRequest, I have to create another record in the Opportunity object and I have to map that record with queried Lead, in the 1st sub request. 

But if there will be no data in the 1st subRequest, then I have to create a record in the Lead object and then I have to query that record again, to map the same with a newly created opportunity in some other subRequest, in the same composite request body. 

So is it possible to create conditional statements in a composite request ?