从同一服务器上的单独数据库联接表时的查询性能

Question

I am trying to make a massive query (Probably a bad idea, but I don't know another way to do this) that pulls data from two separate databases that are on the same server. Here is what I have

    Select Distinct PartDetail.Item_ID+' '+PartDetail.Color+PartDetail.Attachment As ItemCode,
     concat(
      max(case when PartQuality.Quality_Seq = '1' Then Quality.DSC end),' ',
      max(Case When PartQuality.Quality_Seq = '2' then Quality.DSC End),' ',
      max(Case When PartQuality.Quality_Seq = '3' Then Quality.DSC End),' ',
      max(case when PartQuality.Quality_Seq = '4' Then Quality.DSC end),' ',
      max(Case When PartQuality.Quality_Seq = '5' then Quality.DSC End),' ',
      max(Case When PartQuality.Quality_Seq = '6' Then Quality.DSC End),' ',
      max(case when PartQuality.Quality_Seq = '7' Then Quality.DSC end),' ',
      max(Case When PartQuality.Quality_Seq = '8' then Quality.DSC End),' ',
      max(Case When PartQuality.Quality_Seq = '9' Then Quality.DSC End)) As ProdDesc,
      InventoryDB.dbo.ITEM.QtyOnHand
       From SelectDB.dbo.PartDetail
        Join InventoryDB.dbo.ITEM on ITEM.Itemcode = PartDetail.Item_ID+' '+PartDetail.Color+PartDetail.Attachment
        Join SelectDB.dbo.PartQuality on PartQuality.Item_ID = PartDetail.Item_ID
        Join SelectDB.dbo.Quality on Quality.QualityCode = PartQuality.QualityCode
        Join SelectDB.dbo.Part on Part.Item_ID = PartDetails.Item_ID
        Join SelectDB.dbo.PartPrefix on PartPrefix.PrefixCode = Part.PrefixCode
        Join SelectDB.dbo.ProductPart on ProductPart.Item_ID = PartDetail.Item_ID
        Join SelectDB.dbo.Product on Product.Product_ID = ProductPart.Product_ID
        Join SelectDB.dbo.ProductMod on PrdouctMod.ProductMod_ID = Product.ProductMod_ID
        Join SelectDB.dbo.MakeModel on MakeModel.MakeModel_ID = Product.MakeModel_ID
        Join SelectDB.dbo.ProductStyle on ProductStyle.Style_ID = ProductStyle.Style_ID                        
        Join SelectDB.dbo.ProductMake on ProductMake.Make_ID = MakeModel.Make_ID
         Where Product.ModelYear = @YEAR
          And ProductMake.Name = @MAKE
          And MakeModel.Name = @MODEL
          And ProductStyle.DSC = @STYLE
          And ProductMod.DSC = @MOD
          And PartPrefix.DSC = @LOC
           Group By PartDetail.Item_ID+' '+PartDetail.Color+PartDetail.Attachment, ITEM.QtyOnHand

It currently workings but when I added in the following lines to obtain the QtyOnHand field from the InventoryDB, the query went from completing instantly to taking 20-30+ seconds to run.

Select Distinct . . . . InventoryDB.dbo.ITEM.QtyOnHand
From . . . . 
Join InventoryDB.dbo.ITEM on ITEM.Itemcode = PartDetail.Item_ID+' '+PartDetail.Color+PartDetail.Attachment
. . ..
Where . . . . 
Group By . . . . ITEM.QtyOnHand

Since the query runs fine without these lines I figured it must be something with these lines. If I had to guess, it would be the Join InventoryDB.dbo.ITEM on ITEM.Itemcode = PartDetail.Item_ID+' '+PartDetail.Color+PartDetail.Attachment due to having to concatenate those three fields together and then search for matching value, but I'm not sure of anyway around that.

Answer 1

You are probably correct that the string concatenation is slowing things down.

One method is to create a computed column and build an index on it:

alter table PartDetail add ItemCode as (Item_ID + ' ' + Color + Attachment);

create index idx_PartDetail_ItemCode on PartDetail(ItemCode);

The ItemCode column will then be materialized for the table, along with an index. This should greatly speed the processing.