Question

I’ve been banging my head on this one for a while now. I want to achieve this:

SELECT [t2].[nArtKey], [t2].[value] AS [nQty]
FROM (
    SELECT SUM([t0].[nQty]) AS [value], [t1].[nArtKey]
        FROM [vdatStockTransactions] AS [t0]
        INNER JOIN [regArtSKU] AS [t1] ON [t0].[nSKU] = [t1].[nSKU]
        GROUP BY [t1].[nArtKey]
        ) AS [t2]
    INNER JOIN [regArticles] AS [t3] ON [t2].[nArtKey] = [t3].[nArtKey]
    INNER JOIN [regGroupConnector] AS [t4] ON [t2].[nArtKey] = [t4].[nArtKey]
WHERE [t2].[value] > @p0

What I have so far with LINQ gives me pretty much exactly what I want, exept for the quantity…

from trans in context.vdatStockTransactions
join sku in context.regArtSKUs on trans.nSKU equals sku.nSKU
group trans by new { sku.nArtKey } into grp
where grp.Sum(g => g.nQty) > 0
join art in context.regArticles on grp.Key.nArtKey equals art.nArtKey       
join ca in context.regGroupConnectors on grp.Key.nArtKey equals ca.nArtKey
select new
{
    nArtKey = grp.Key.nArtKey,
    //nQty = grp.Sum(g => g.nQty)
};

However, if I uncomment nQty I get this:

SELECT [t7].[nArtKey], [t7].[value] AS [nQty]
FROM (
    SELECT [t3].[nArtKey], (
        SELECT SUM([t5].[nQty])
        FROM [vdatStockTransactions] AS [t5]
        INNER JOIN [regArtSKU] AS [t6] ON [t5].[nSKU] = [t6].[nSKU]
        WHERE [t2].[nArtKey] = [t6].[nArtKey]
        ) AS [value], [t2].[value] AS [value2]
    FROM (
        SELECT SUM([t0].[nQty]) AS [value], [t1].[nArtKey]
        FROM [vdatStockTransactions] AS [t0]
        INNER JOIN [regArtSKU] AS [t1] ON [t0].[nSKU] = [t1].[nSKU]
        GROUP BY [t1].[nArtKey]
        ) AS [t2]
    INNER JOIN [regArticles] AS [t3] ON [t2].[nArtKey] = [t3].[nArtKey]
    INNER JOIN [regGroupConnector] AS [t4] ON [t2].[nArtKey] = [t4].[nArtKey]
    ) AS [t7]
WHERE [t7].[value2] > @p0

Why does it create that extra subquery and is there any way that I could avoid it? It makes quite a big difference in performance so I really would like to figure this out. All I want is to use the quantity ([t2].[value]) and get it into the SELECT statement.

That extra subquery only exists when there are more than one join after group by so if I remove either then the query generates the expected SQL.

NOTE: I stripped down the original query to just keep the parts that are generating this behavior so it would be easier to follow.

Answer 1

I haven’t tested this, but this might do the trick:

var quantities =
    from trans in context.vdatStockTransactions
    group trans by trans.SKU.nArtKey into grp
    select new
    {
        nQty = grp.Sum(g => g.nQty), 
        nArtKey = grp.Key 
    };

var results =
    from quantity in quantities
    join art in context.regArticles
        on quantity.nArtKey equals art.nArtKey       
    join ca in context.regGroupConnectors 
        on quantity.nArtKey equals ca.nArtKey
    where quantity.nQty > 0
    select quantity;