how to perform count using nested select in a select statement - mysql

Question

So here is the issue. I'm trying to write a new fillrate report because the one built in is not good enough... I'm trying to run a single select statement to return both, a count of how many times an item was ordered for a specific month, and then also a count of how many times it was invoiced/shipped in full.
This code is obviously wrong, I also currently have it restricted to only look at AUG of 2015, but that is just to simplify results during testing.
I can't figure out how to do the 2nd count... This is what I was trying (brain stuck on old for each loop logic):
select inv_mast.item_id,
inv_mast.item_desc,
"YEAR" = year(oe_line.required_date),
"MONTH" = month(oe_line.required_date),
"ORDERS" = count(1),
"HITS" = (
select count(1)
from invoice_line
where invoice_line.order_no = oe_line.order_no
and invoice_line.oe_line_number = oe_line.line_no
and invoice_line.qty_shipped = oe_line.qty_ordered
)
from oe_line,
inv_mast,
inv_loc
where inv_mast.inv_mast_uid = oe_line.inv_mast_uid
and inv_mast.delete_flag = 'N'
and inv_mast.inv_mast_uid = inv_loc.inv_mast_uid
and inv_loc.location_id = '101'
and year(oe_line.required_date) = '2015'
and month(oe_line.required_date) = '8'
group by inv_mast.item_id,
inv_mast.item_desc,
year(oe_line.required_date),
month(oe_line.required_date)
order by inv_mast.item_id

Answer 1

To me it would seem like you could rewrite the query to use a left join on the invoice_line table instead. Without any proper test data I can't guarantee it is correct, but I think it should be.
Besides the left join I also changed to explicit joins and moved the aliases as I don't think MySQL supports the alias = column syntax.
select inv_mast.item_id,
inv_mast.item_desc,
year(o.required_date) as "YEAR",
month(o.required_date) as "MONTH",
count(1) as "ORDERS",
count(invoice_line.order_no) as "HITS"
from oe_line o
join inv_mast on inv_mast.inv_mast_uid = o.inv_mast_uid
join inv_loc on inv_mast.inv_mast_uid = inv_loc.inv_mast_uid
left join invoice_line on invoice_line.order_no = o.order_no
and invoice_line.oe_line_number = o.line_no
and invoice_line.qty_shipped = o.qty_ordered
where inv_mast.delete_flag = 'N'
and inv_loc.location_id = '101'
and year(o.required_date) = '2015'
and month(o.required_date) = '8'
group by inv_mast.item_id,
inv_mast.item_desc,
year(o.required_date),
month(o.required_date)
order by inv_mast.item_id;