How to optimize sql queries and get rid of the cycle?

Question

MySQL

I have a query like:

select a.field1, a.field2, a.field3, b.field1, b.field2
from table1 as a
left join table2 as b on a.field1 = b.field1
where ...

the data from it is written to the object.
Next, you need to add data to the object from other tables.
currently did this:

foreach $obj as o {
   select c.field1
   from table3 as c
   left join table4 as d on c.field2 = d.field2
   where c.field3 = a.field1
}

The code is somewhat exaggerated, but the meaning, I think, is clear.
it is clear that a bunch of calls to the database in a cycle loads the database
how to simplify it?

Answer 1

What prevents you from expanding the original query with the necessary joins and getting exactly the right list?

Answer 2

From the result of the first query, select all a.field1 into the array.
Run the second query with a selection of all rows through where c.field3 in (array a.field1)
Total 2 queries
Or immediately join into one, what is the problem? (Depending on how many rows there should be in this cyclic query)