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POLINQ to SQL complex query problem
 

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    <p>I have 3 tables: Principal (Principal_ID, Scale), Frequency (Frequency_ID, Value) and Visit (Visit_ID, Principal_ID, Frequency_ID). I need a query which returns all principals (in the Principal table), and for each record, query the capacity required for that principal, calculated as below:</p> <pre><code>Capacity = (Principal.Scale == 0 ? 0 : (Frequency.Value == 1 ? 1 : Frequency.Value * 1.8) / Principal.Scale) </code></pre> <p>I'm using LINQ to SQL, so here is the query:</p> <pre><code>from Principal p in ShopManagerDataContext.Instance.Principals let cap = ( from Visit v in p.Visits let fqv = v.Frequency.Value select (p.Scale != 0 ? ((fqv == 1.0f ? fqv : fqv * 1.8f) / p.Scale) : 0) ).Sum() select new { p, Capacity = cap }; </code></pre> <p>The generated TSQL:</p> <pre><code>SELECT [t0].[Principal_ID], [t0].[Name], [t0].[Scale], ( SELECT SUM( (CASE WHEN [t0].[Scale] &lt;&gt; @p0 THEN ( (CASE WHEN [t2].[Value] = @p1 THEN [t2].[Value] ELSE [t2].[Value] * @p2 END)) / (CONVERT(Real,[t0].[Scale])) ELSE @p3 END)) FROM [Visit] AS [t1] INNER JOIN [Frequency] AS [t2] ON [t2].[Frequency_ID] = [t1].[Frequency_ID] WHERE [t1].[Principal_ID] = [t0].[Principal_ID] ) AS [Capacity] FROM [Principal] AS [t0] </code></pre> <p>And the error I get:</p> <pre><code>SqlException: Multiple columns are specified in an aggregated expression containing an outer reference. If an expression being aggregated contains an outer reference, then that outer reference must be the only column referenced in the expression. </code></pre> <p>And ideas how to solve this, if possible, in one query?</p> <p>Thank you very much in advance!</p>
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