How to update table with column set NULL in codeigniter

use this to set null column.it will work, dont forget add false on third parameter SET on active record

$this->db->set('id_parent', 'NULL', false);

you can try this code in 'model', hope it'll work:

public function update_std_marks($id_user) {    $this->db->set('id_parent', null);    $this->db->where('id_user', $id_user);    $this->db->update('user');}

I was curious so I wanted to see how CodeIgniter's Active Record would handle different variations of syntax when working with a null value. I'll map out several test cases for where() and set() method calls.

Battery of where() tests:

1. ->where('col', null)                  // `col` IS NULL

2. ->where('col', null, false)           // col IS NULL

3. ->where('col', 'NULL')                // `col` = 'NULL'

4. ->where('col', 'NULL', false)         // col =  NULL

5. ->where('col IS NULL')                // `col` IS NULL

6. ->where('col IS NULL', null)          // `col` IS NULL

7. ->where('col IS NULL', null, false)   // col IS NULL

8. ->where('col', 'IS NULL')             // `col` 'IS NULL'

9. ->where('col', 'IS NULL', false)      // col = IS NULL

Properly quoted and formed: #1, #5, #6 (recommended)
Logically formed, but not quoted: #2, #7 (not recommended)
Inappropriate rendered syntax: #3, #4, #8, #9 (do not use)

Battery of set() tests:

1. ->set('col', null)                  // `col` = NULL

2. ->set('col', null, false)           // col =

3. ->set('col', 'NULL')                // `col` = 'NULL'

4. ->set('col', 'NULL', false)         // col = NULL

5. ->set('col IS NULL')                // `col IS` `NULL` = ''

6. ->set('col IS NULL', null)          // `col IS` `NULL` = NULL

7. ->set('col IS NULL', null, false)   // col IS NULL =

8. ->set('col', 'IS NULL')             // `col` = 'IS NULL'

9. ->set('col', 'IS NULL', false)      // col = IS NULL

Properly quoted and formed: #1 (recommended)
Logically formed, but not quoted: #4 (not recommended)
Inappropriate rendered syntax: #2, #3, #5, #6, #7, #8, #9 (do not use)