I have 3 tables,
itemmaster
|--------|----------|
| id | name |
|--------|----------|
| 1 | Pizza |
|--------|----------|
| 2 | Burger |
|--------|----------|
| 3 | Pepsi |
---------------------
order
|--------|----------|
|orderid | date |
|--------|----------|
| 1 | 1-1-11 |
|--------|----------|
| 2 | 2-1-11 |
|--------|----------|
| 3 | 3-1-11 |
---------------------
orderdetails
|--------|-------------|---------|---------|
| id | orderid |itemid |quantity |
|--------|-------------|---------|---------|
| 1 | 1 | 1 | 10 |
|--------|-------------|---------|---------|
| 2 | 1 | 2 | 20 |
|--------|-------------|---------|---------|
| 3 | 2 | 1 | 10 |
-------------------------------------------
I want to join these 3 tables to get quantity of items of an order that placed on a particular date. What I have tried is:
$this->db->from('itemmaster');
$this->db->join('orderdetails', 'orderdetails.itemid= itemmaster.id','left');
$this->db->join('order', 'order.orderid= orderdetails.orderid');
$this->db->where('order.date',"1-1-11");
$query = $this->db->get();
I got result as:
Pizza------ 10
Burger------10
What I want is:
Pizza-------10
Burger------20
Pepsi-------0
If changing the all the joins to left joins, you can always do it in two separate query and do a union between the two of them. One would get all the lines that actualy have a quantity and the other would get the rests and put them toguether.
It would look a bit like this. there might be some synthax error, but you'll have to rewrite it in php anyway:
p.s. to add up the quantities, you can use sum()
Select itemmaster.name, orderdetails.quantity from itemmaster
left join orderdetails on orderdetails.itemid = itemmaster.id
left join order on order.orderid = orderdetails.orderid
where order.date = '1-1-11'
group by itemmaster.name
Union
Select itemmaster.name, '0' as quantity From itemmaster
except (Select itemmaster.name, orderdetails.quantity from itemmaster
left join orderdetails on orderdetails.itemid = itemmaster.id
left join order on order.orderid = orderdetails.orderid
where order.date = '1-1-11'
group by itemmaster.name)
group by itemmaster.name
hope this helps ! good luck