Mysql Query speed takes 50 seconds - mysql

Question

I have the below Query which takes around 50 seconds to run, is there a way to make it faster? i have not done any indexing yet and will try to do that in the near future but i am still new in this. the problem is not using indexing.
Select stock.StockID As StockID,
stock.BinLocation As BinLocation,
stock.StockCode As StockCode,
stock.Descr As Descr,
stock.Currency As Currency,
stock.Notes As Notes,
stocklocations.Quantity As Quantity,
stocklocations.SLNID As SLNID,
stock.ConditionA As ConditionA,
stocklocationsname.SLN As SLN,
stock.DateAdded As DateAdded,
(Case When (stock.Currency = 'Euro') Then (1.05 * stock.unitprice)
When (stock.Currency = 'GBP') Then (1.24 * stock.unitprice)
When (stock.Currency = 'USD') Then (1 * stock.unitprice) End) As unitprice,
stock.DepName As DepName,
stockhistory.POID As POID,
stock.POID As POID1,
stock.PartNumber As PartNumber,
vender.VendorName As VendorName,
equiptype.EQName As EQName,
groupname.Name As Name
From ((((((stock
Join stocklocations On stock.StockID = stocklocations.StockID)
Join stocklocationsname On stocklocations.SLNID = stocklocationsname.SLNID)
Left Join stockhistory On stockhistory.SHID = (Select Min(stockhistory.SHID)
From stockhistory Where stockhistory.StockID = stock.StockID))
Left Join po On stockhistory.POID = po.POID)
Left Join vender On po.Vender = vender.VendorID)
Left Join equiptype On stock.EquipType = equiptype.EquipTypeID)
Left Join groupname On stock.GroupNameID = groupname.GroupNameID
Where stocklocations.Quantity > 0 And stock.Status <> 'obsolete'

Answer 1

You should probably have an index on stockhistory.StockID:
ALTER TABLE stockhistory ADD INDEX (StockID);
That should speed up the subqueries on stockhistory. Alternatively, since you're retrieving the minimum value of SHID, you might include that column in the index as well:
ALTER TABLE stockhistory ADD INDEX (StockID, SHID);
Adding indexes does not create any restrictions or logical constraints (with the exception of unique indexes). However, as stated in 8.3 Optimization and Indexes from the MySQL documentation:
Although it can be tempting to create an indexes for every possible column used in a query, unnecessary indexes waste space and waste time for MySQL to determine which indexes to use. Indexes also add to the cost of inserts, updates, and deletes because each index must be updated. You must find the right balance to achieve fast queries using the optimal set of indexes.
Figuring out which indexes to create is something of an art. A good start is to investigate query execution with EXPLAIN, as described in 8.8.1 Optimizing Queries with EXPLAIN.

Answer 2

1 ) Remove unuseful () and avoid nested left join
2 ) don't use where fo column involved in left join because this way became inner join
3 ) instead of a subselect try using a join of for the min value related to stockid in stockhistory
Select
stock.StockID As StockID,
stock.BinLocation As BinLocation,
stock.StockCode As StockCode,
stock.Descr As Descr,
stock.Currency As Currency,
stock.Notes As Notes,
stocklocations.Quantity As Quantity,
stocklocations.SLNID As SLNID,
stock.ConditionA As ConditionA,
stocklocationsname.SLN As SLN,
stock.DateAdded As DateAdded,
Case When stock.Currency = 'Euro' Then 1.05 * stock.unitprice
When stock.Currency = 'GBP' Then 1.24 * stock.unitprice
When stock.Currency = 'USD' Then 1 * stock.unitprice End As unitprice,
stock.DepName As DepName,
stockhistory.POID As POID,
stock.POID As POID1,
stock.PartNumber As PartNumber,
vender.VendorName As VendorName,
equiptype.EQName As EQName,
groupname.Name As Name
From stock
Join stocklocations On stock.StockID = stocklocations.StockID
and stocklocations.Quantity > 0
And stock.Status <> 'obsolete'
Join stocklocationsname On stocklocations.SLNID = stocklocationsname.SLNID
Left Join (
Select stockhistory.StockID, Min(stockhistory.SHID)
From stockhistory
group by stockhistory.StockID ) t_h on t_h StockID = stockhistory.StockID
Left Join po On stockhistory.POID = po.POID
Left Join vender On po.Vender = vender.VendorID
Left Join equiptype On stock.EquipType = equiptype.EquipTypeID
Left Join groupname On stock.GroupNameID = groupname.GroupNameID
be sure you have also proper index on the tables and columns involved in join

Answer 3

Try without brackets which you write along joins and FROM.
Select stock.StockID As StockID,
stock.BinLocation As BinLocation,
stock.StockCode As StockCode,
stock.Descr As Descr,
stock.Currency As Currency,
stock.Notes As Notes,
stocklocations.Quantity As Quantity,
stocklocations.SLNID As SLNID,
stock.ConditionA As ConditionA,
stocklocationsname.SLN As SLN,
stock.DateAdded As DateAdded,
(Case When (stock.Currency = 'Euro') Then (1.05 * stock.unitprice)
When (stock.Currency = 'GBP') Then (1.24 * stock.unitprice)
When (stock.Currency = 'USD') Then (1 * stock.unitprice) End) As unitprice,
stock.DepName As DepName,
stockhistory.POID As POID,
stock.POID As POID1,
stock.PartNumber As PartNumber,
vender.VendorName As VendorName,
equiptype.EQName As EQName,
groupname.Name As Name
From stock
Join stocklocations On stock.StockID = stocklocations.StockID
Join stocklocationsname On stocklocations.SLNID = stocklocationsname.SLNID
Left Join stockhistory On stockhistory.SHID = (Select Min(stockhistory.SHID) From stockhistory Where stockhistory.StockID = stock.StockID)
Left Join po On stockhistory.POID = po.POID
Left Join vender On po.Vender = vender.VendorID
Left Join equiptype On stock.EquipType = equiptype.EquipTypeID
Left Join groupname On stock.GroupNameID = groupname.GroupNameID
Where stocklocations.Quantity > 0 And stock.Status <> 'obsolete'

Answer 4

how much time it takes to execute without this?
Left Join stockhistory On stockhistory.SHID = (Select Min(stockhistory.SHID)
From stockhistory Where stockhistory.StockID = stock.StockID))
If it takes 5-6 secs, then you should convert this min SHID group by StockID to a view, and join with the view first, then stockhistory itself to get the stockhistory.POID