Types of SQL statements swallowed by PG's engine

I wonder if they exist and from where could you get a copy of the
list of Types of SQL statements that PG's engine would digest

I think there should be such a list which I would use to model
hierarchical data structures for each of the complaint statements

Say you have a statement like:

SELECT USERS, PHONE WHERE ST='NY' AND PHONE NOT NULL;

For example, this very basic statement could translate to a DS in
Java looking like the following:

// __
class _2a{
public String a00;
public String a02;
}

// __
class DS00{
public String St;
public IsPhoneNull IsPh;
public ArrayList<_2a> AL_2a;
// __
DS00(){ AL_2a = new ArrayList<_2a>(); }
}// DS00

// __
Then your could would look like:

DS00 DS = new DS00();
DS.St = "NY";
DS.IsPhoneNull = false;

_2a a2 = new _2a();
a2.a00 = "Jones";
a2.a02 = "(213) 456-3345";
AL_2a.add(a2);
. . .

This DS would just be a hierarchical object graph

Of course things get complicated when you have such things as joins
and nested queries, I just gave you a complete example for you to see
exactly what I mean

Do you know of any similar project in Java (, ANSI C or CPP)?

Where could I get such a list?

Are there data samples for stress testing PG tables?

Thanks
lbrtchx