Codeigniter查询，用于选择多列总和，每行的条件为

Question

I have made this function to get sum of population percent based on group_id as 1,2 and 3 but its not working

public function ethnicity($value='')
        {
            $this->db->select('SUM(population_percent) as p1 where group_id=1,SUM(population_percent) as p2 where group_id=2,SUM(population_percent) as p3 where group_id=3', FALSE);
            $this->db->from('ethnic_group');
            $data=$this->db->get()->row_array();
                return $data;
        }

Answer 1

When you use $this->db->select() you are writing the 'select' part of a query. To write the 'where' you should use $this->db->where('group_id=3') .

In case you want to write an entire query and tell CodeIgniter to run it, you can use $this->db->query($sql) with $sql beign the actual query you want to run as seen in the documentation here .

So I think it should look something like this:

 $sql = 'your query here';
 $data = $this->db->query($sql)->row_array();
 return $data;

Answer 2

You need to use IF or CASE when need to do sum with this type of condition

Use this query

public function ethnicity($value='')
{
    $sql = "SELECT  
              SUM(CASE WHEN group_id='1' THEN population_percent ELSE 0 END) p1,
              SUM(CASE WHEN Type='2' THEN population_percent ELSE 0 END) p2,
              SUM(CASE WHEN Type='3' THEN population_percent ELSE 0 END) p3,
            FROM ethnic_group LIMIT 1";


    $data = $this->db->query($sql)->row_array();
    return $data;
}