Mysql limit just for the null rows of a certain column

Question

I have something like this $SQL = "SELECT * FROM profile_comments WHERE name = '$username' LIMIT $offset, $rowsperpage"; but I want to know if it's possible to limit the result just for the null rows of a certain column?

Exemple

$SQL = "SELECT * FROM profile_comments WHERE name = '$username' LIMIT table is NULL 5, 10"; 

profile_comments

id | parent_id |  name |    text    | datetime
-------------------------------------------------
 1 |   null    | Netra |  Bla bla   | 00.00.0000
 2 |    1      | Netra |  Bla bla   | 00.00.0000
 3 |    1      | Netra |  Bla bla   | 00.00.0000
 4 |   null    | Netra |  Bla bla   | 00.00.0000
 5 |    4      | Netra |  Bla bla   | 00.00.0000

Answer 1

You need to pud that condition in the WHERE clause, not after the limit clause. How about this?

$SQL = "SELECT * 
        FROM profile_comments 
        WHERE name = '$username' AND  
              `table` is NULL 
        LIMIT 5, 10";

The answer:

SELECT * FROM profile_comments WHERE PARENT_ID IS NOT NULL UNION SELECT * FROM profile_comments WHERE PARENT_ID IS NULL GROUP BY PARENT_ID;