在表格中使用null值在codeigniter中连接3个表

Question

如果我使用加入然后显示空查询，我想要来自3表和费用pericualr字段批次ID和学生ID的数据可能是空白的。

$this->db->select('*');
$this->db->from('fees_perticular');
$this->db->join('fee_cat', 'fees_perticular.fee_cat = fee_cat.id');
$this->db->join('batch', 'fees_perticular.batch= batch.id');
$this->db->join('stud_cat', 'fees_perticular.sud_cat = stud_cat.id');

$query = $this->db->get();
id |    fee_cat |   particular_name |   desc     |all |batch|admission|sud_cat|amount
1  |    1       |     Annual Fees   |Annual Fees |all |-    |-        |-      |2000
2  |    2       |     Tuition Fees  |Tuition Fees|-   |3    |-        |-      |1000
3  |    1       |     Tuition Fees  |vccvv       |-   |1    |-        |-      |1000

Answer 1

请试试这个

$this->db->select('*')
$this->db->join('fee_cat','fees_particular.fee_cat=fee_cat.fee_cat_id','LEFT')
$this->db->join('batch','fees_particular.batch=batch.batch_id','LEFT')
$this->db->join('stud_cat','fees_particular.stud_cat=stud_cat.stud_cat_id','LEFT')
$this->db->get('fees_particular');