Golang Route for insert – PrepareContext error

sorry, not enough reputation to post images. I have 3 SQL tables:

x1: {‘a’:1,2,3,4,5},

x2: {‘c’:1,1,1,2,2,3,3, ‘d’:1,3,5,1,3,1,1},

x3: {‘b’:1,3,5}

The query is:

select a from x1 
where not exists (
  select * from x3
  where not exists (
    select *
    from x2
    where x1.a = x2.c and x3.b=x2.d

The result from the following query is ‘1‘, but I can’t understand what are the steps taken to get to that result.

What is being returned in which subquery?