SQLException : Incorrect syntax near the keyword 'UNION'

Linq query with Union and OrderBy does not translate correctly.

Simple:

_context.Subjects.Where(s => !(s is Group))
                  .OrderBy(o => o.Created) 
                   .Take(10)
                   .Union(_context.Subjects.Where(s => s is Group)
                                            .OrderBy(o => o.Created)
                                            .Take(10))
                    .ToList();

This will be translate to =>

Select 
Where
OrderBy  -Error ( select must be in subquery)
UNION 
Select
Where
Order by -Error ( select must be in subquery)

Incorrect syntax near the keyword ‘UNION’

SELECT TOP(@__p_0) [s].[SubjectId], [s].[Address], [s].[Changed], [s].[Created]
FROM [Subjects] AS [s]
WHERE ([s].[Discriminator] IN (N'PhysicalPerson', N'Company', N'PrivateCompany', N'Group') AND (CASE
    WHEN @__ef_filter__p_0 = CAST(1 AS bit) THEN CAST(1 AS bit)
    ELSE CASE
        WHEN (CAST(1 AS bit) = CAST(0 AS bit)) AND ([s].[IsDeleted] <> CAST(1 AS bit)) THEN CAST(1 AS bit)
        ELSE CAST(0 AS bit)
    END
END = CAST(1 AS bit))) AND ([s].[Discriminator] <> N'Group')
ORDER BY [s].[Created]
UNION
SELECT TOP(@__p_0) [s0].[SubjectId], [s0].[Address], [s0].[Changed], [s0].[Created]
FROM [Subjects] AS [s0]
WHERE ([s0].[Discriminator] IN (N'PhysicalPerson', N'Company', N'PrivateCompany', N'Group') AND (CASE
    WHEN @__ef_filter__p_0 = CAST(1 AS bit) THEN CAST(1 AS bit)
    ELSE CASE
        WHEN (CAST(1 AS bit) = CAST(0 AS bit)) AND ([s0].[IsDeleted] <> CAST(1 AS bit)) THEN CAST(1 AS bit)
        ELSE CAST(0 AS bit)
    END
END = CAST(1 AS bit))) AND ([s0].[Discriminator] = N'Group')
ORDER BY [s0].[Created]

EF Core version: Database provider: (e.g. Microsoft.EntityFrameworkCore.SqlServer) Target framework: (e.g. .NET Core 3.0) Operating system: IDE: (e.g. Visual Studio 2019 16.3)

[smitpatel]

SELECT TOP(1) [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
FROM [Customers] AS [c]
ORDER BY [c].[ContactName]
UNION
SELECT TOP(1) [c0].[CustomerID], [c0].[Address], [c0].[City], [c0].[CompanyName], [c0].[ContactName], [c0].[ContactTitle], [c0].[Country], [c0].[Fax], [c0].[Phone], [c0].[PostalCode], [c0].[Region]
FROM [Customers] AS [c0]
ORDER BY [c0].[ContactName]

Above is invalid SQL but when you push down the whole thing it’s valid. :trollface:

SELECT *
FROM (
	SELECT TOP(1) [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
	FROM [Customers] AS [c]
	ORDER BY [c].[ContactName]
	UNION
	SELECT TOP(1) [c0].[CustomerID], [c0].[Address], [c0].[City], [c0].[CompanyName], [c0].[ContactName], [c0].[ContactTitle], [c0].[Country], [c0].[Fax], [c0].[Phone], [c0].[PostalCode], [c0].[Region]
	FROM [Customers] AS [c0]
	ORDER BY [c0].[ContactName]
) as t

[roji]

Apologies, I mistested the above - in SQL Server ORDER BY is of course OK in subqueries as long as TOP is present as well. So it’s indeed possible to translate this by pushing down to a subquery in the SQL Server and Sqlite case (again, in the PostgreSQL case an actual subquery isn’t necessary, only parentheses).