Sqlite select query take too time? - sql

Question

I was developed a pos software with sqlite database.It was fined in early but now it is too slow with many data storage.Some of select view query take at least 3 minutes for only read in c# data reader.It is so bad.It may be wrong in database table structure.The worst performance views is following:
Firstly i have Stocks Table,Storage Storage Table,Purchase Receive Items Table and Sale Voucher Items.
Stock table has 3000 rows.Stock Storage table has 4600 rows. Purchase Receive Items table has 4500 rows and sale voucher items table has 130,00 rows.I was created view for show sum of purchase item and sum of sale items like that=>
select
Sto.stockcode,
Sto.StockName,
IfNull((select sum(ss.OpeningQty) from StockStorages ss
where ss.stockid=Sto.stockid and ss.status='A'),0) [OpeningQty],
IfNull((select sum(pur.qty) from purchasereceiveitems pur
where pur.stockid=Sto.stockid and pur.status='A'),0) [Purqty],
IfNull((select sum(svi.qty) from salevoucheritems svi
where svi.stockid=Sto.stockid and svi.status='A'),0) [Salqty],
IfNull((select sum(sti.qty) from StockTransactionItems sti
where sti.stockid=Sto.stockid and sti.status='A'),0) [Transactionqty],
IfNull((select sum(ss.CurrentQty) from StockStorages ss
where ss.stockid=Sto.stockid and ss.status='A'),0) [CurrentQty]
from stocks Sto
where Sto.status='A'
group by Sto.StockCode
How can i improve my structure or my code.Please advice me.

Answer 1

Turn your correlated subqueries (O(n^2) performance) into left joins like this:
select
s.stockcode,
s.stockname,
ifnull(a.opening_qty, 0) opening_qty,
ifnull(b.Purqty, 0) Purqty,
ifnull(c.salqty, 0) salqty,
ifnull(d.Transactionqty, 0) Transactionqty,
ifnull(e.CurrentQty, 0) CurrentQty
from StockCode s
left join (select
stockid,
sum(OpeningQty) opening_qty
from StockStorages
where status='A'
group by stockid) a on s.stockid = a.stockid
left join (select
stockid,
sum(qty) Purqty
from purchasereceiveitems
where status='A'
group by stockid) b on s.stockid = b.stockid
(select
stockid,
sum(qty) salqty
from salevoucheritems
where status='A'
group by stockid) c on s.stockid = c.stockid
(select
stockid,
sum(qty) Transactionqty
from StockTransactionItems
where status='A'
group by stockid) d on s.stockid = d.stockid
(select
stockid,
sum(CurrentQty) CurrentQty
from StockStorages
where status='A'
group by stockid) e on s.stockid = e.stockid
where s.status = 'A';

Answer 2

This query can be sped up by indexing the columns that are used for lookups, so that the subqueries no longer need to search the entire table for each single value:
CREATE INDEX StockStorages_ss ON StockStorages (stockid, status);
CREATE INDEX purchasereceiveitems_ss ON purchasereceiveitems (stockid, status);
CREATE INDEX salevoucheritems_ss ON salevoucheritems (stockid, status);
CREATE INDEX StockTransactionItems_ss ON StockTransactionItems(stockid, status);
CREATE INDEX StockStorages_ss ON StockStorages (stockid, status);