Codeigniter Active record And Or combinations in where clause with multiple & nested groups - codeigniter

Question

I have a complex SQL query and I want to implement it through Active Records. This query has several AND / OR clauses grouped together with another criteria. I have gone through various articles where they said that we can use group_start() and group_end() but I am wondering if a group can be started inside another group too? The resulting serial numbers needs to be excluded from the result set to be produced by the outer query. Actually I tried using Join here, but it didn't work. Any working idea regarding joins here will be appreciable too.
As you can see in the query below, I have used double round brackets to represent multiple groups inside a group.
The resulting serial numbers needs to be excluded from the results of outer query too. Please tell me what will be its Codeigniter Active Record equivalent code.
select * from table2 WHERE NOT table2.serial IN (select columnname from table where ((col < val and val < col) or (col < val and val < col) or(val=col and val=col)) AND incol=intval AND intcol=intval)
Here, col is the column name, val is a value of DATE type, intval is
an Integer value

Answer 1

Try this syntax
$this->db->select("*")->from("table");
$this->db->group_start();
$this->db->group_start();
$this->db->where("val <",'col');
$this->db->where("val <",'col');
$this->db->group_end();
$this->db->or_group_start();
$this->db->or_where("val <",'col');
$this->db->where("val <",'col');
$this->db->group_end();
$this->db->or_group_start();
$this->db->or_where("val ",'col');
$this->db->where("val ",'col');
$this->db->group_end();
$this->db->group_end();
$this->db->where("incol ",'intval');
$this->db->where("incol ",'intval');
$this->db->get();
$last_query = $this->db->last_query();
$this->db->select('*')->from('table2');
$this->db->where_not_in('serial',$last_query);
$this->db->get();
echo $this->db->last_query();
The query string produced by the above is
SELECT * FROM `table2` WHERE
`serial` NOT IN(
SELECT columnname FROM `table` WHERE
(
(`val` < 'col' AND `val` < 'col') OR
(`val` < 'col' AND `val` < 'col') OR
(`val` = 'col' AND `val` = 'col')
) AND `incol` = 'intval' AND `incol` = 'intval'
);