Recursive query with outer joins?

Question

I'm attempting the following query,

DECLARE @EntityType varchar(25)
SET @EntityType = 'Accessory';

WITH Entities (
        E_ID, E_Type,
        P_ID, P_Name, P_DataType, P_Required, P_OnlyOne,
        PV_ID, PV_Value, PV_EntityID, PV_ValueEntityID,
        PV_UnitValueID, PV_UnitID, PV_UnitName, PV_UnitDesc, PV_MeasureID, PV_MeasureName, PV_UnitValue,
        PV_SelectionID, PV_DropDownID, PV_DropDownName, PV_DropDownOptionID, PV_DropDownOptionName, PV_DropDownOptionDesc,
        RecursiveLevel
    )
AS
(
    -- Original Query
    SELECT dbo.Entity.ID AS E_ID, dbo.EntityType.Name AS E_Type,
    dbo.Property.ID AS P_ID, dbo.Property.Name AS P_Name, DataType.Name AS P_DataType, Required AS P_Required, OnlyOne AS P_OnlyOne,
    dbo.PropertyValue.ID AS PV_ID, dbo.PropertyValue.Value AS PV_Value, dbo.PropertyValue.EntityID AS PV_EntityID, dbo.PropertyValue.ValueEntityID AS PV_ValueEntityID,
    dbo.UnitValue.ID AS PV_UnitValueID, dbo.UnitOfMeasure.ID AS PV_UnitID, dbo.UnitOfMeasure.Name AS PV_UnitName, dbo.UnitOfMeasure.Description AS PV_UnitDesc, dbo.Measure.ID AS PV_MeasureID, dbo.Measure.Name AS PV_MeasureName, dbo.UnitValue.UnitValue AS PV_UnitValue,
    dbo.DropDownSelection.ID AS PV_SelectionID, dbo.DropDown.ID AS PV_DropDownID, dbo.DropDown.Name AS PV_DropDownName, dbo.DropDownOption.ID AS PV_DropDownOptionID, dbo.DropDownOption.Name AS PV_DropDownOptionName, dbo.DropDownOption.Description AS PV_DropDownOptionDesc,
    0 AS RecursiveLevel
    FROM dbo.Entity
    INNER JOIN dbo.EntityType ON dbo.EntityType.ID = dbo.Entity.TypeID
    INNER JOIN dbo.Property ON dbo.Property.EntityTypeID = dbo.Entity.TypeID
    INNER JOIN dbo.PropertyValue ON dbo.Property.ID = dbo.PropertyValue.PropertyID AND dbo.PropertyValue.EntityID = dbo.Entity.ID
    INNER JOIN dbo.DataType ON dbo.DataType.ID = dbo.Property.DataTypeID
    LEFT JOIN dbo.UnitValue ON dbo.UnitValue.ID = dbo.PropertyValue.UnitValueID
    LEFT JOIN dbo.UnitOfMeasure ON dbo.UnitOfMeasure.ID = dbo.UnitValue.UnitOfMeasureID
    LEFT JOIN dbo.Measure ON dbo.Measure.ID = dbo.UnitOfMeasure.MeasureID
    LEFT JOIN dbo.DropDownSelection ON dbo.DropDownSelection.ID = dbo.PropertyValue.DropDownSelectedID
    LEFT JOIN dbo.DropDownOption ON dbo.DropDownOption.ID = dbo.DropDownSelection.SelectedOptionID
    LEFT JOIN dbo.DropDown ON dbo.DropDown.ID = dbo.DropDownSelection.DropDownID
    WHERE dbo.EntityType.Name = @EntityType
    UNION ALL
    -- Recursive Query?
    SELECT E2.E_ID AS E_ID, dbo.EntityType.Name AS E_Type,
    dbo.Property.ID AS P_ID, dbo.Property.Name AS P_Name, DataType.Name AS P_DataType, Required AS P_Required, OnlyOne AS P_OnlyOne,
    dbo.PropertyValue.ID AS PV_ID, dbo.PropertyValue.Value AS PV_Value, dbo.PropertyValue.EntityID AS PV_EntityID, dbo.PropertyValue.ValueEntityID AS PV_ValueEntityID,
    dbo.UnitValue.ID AS PV_UnitValueID, dbo.UnitOfMeasure.ID AS PV_UnitID, dbo.UnitOfMeasure.Name AS PV_UnitName, dbo.UnitOfMeasure.Description AS PV_UnitDesc, dbo.Measure.ID AS PV_MeasureID, dbo.Measure.Name AS PV_MeasureName, dbo.UnitValue.UnitValue AS PV_UnitValue,
    dbo.DropDownSelection.ID AS PV_SelectionID, dbo.DropDown.ID AS PV_DropDownID, dbo.DropDown.Name AS PV_DropDownName, dbo.DropDownOption.ID AS PV_DropDownOptionID, dbo.DropDownOption.Name AS PV_DropDownOptionName, dbo.DropDownOption.Description AS PV_DropDownOptionDesc,
    (RecursiveLevel + 1)
    FROM Entities AS E2
    INNER JOIN dbo.Entity ON dbo.Entity.ID = E2.PV_ValueEntityID
    INNER JOIN dbo.EntityType ON dbo.EntityType.ID = dbo.Entity.TypeID
    INNER JOIN dbo.Property ON dbo.Property.EntityTypeID = dbo.Entity.TypeID
    INNER JOIN dbo.PropertyValue ON dbo.Property.ID = dbo.PropertyValue.PropertyID AND dbo.PropertyValue.EntityID = E2.E_ID
    INNER JOIN dbo.DataType ON dbo.DataType.ID = dbo.Property.DataTypeID
    INNER JOIN dbo.UnitValue ON dbo.UnitValue.ID = dbo.PropertyValue.UnitValueID
    INNER JOIN dbo.UnitOfMeasure ON dbo.UnitOfMeasure.ID = dbo.UnitValue.UnitOfMeasureID
    INNER JOIN dbo.Measure ON dbo.Measure.ID = dbo.UnitOfMeasure.MeasureID
    INNER JOIN dbo.DropDownSelection ON dbo.DropDownSelection.ID = dbo.PropertyValue.DropDownSelectedID
    INNER JOIN dbo.DropDownOption ON dbo.DropDownOption.ID = dbo.DropDownSelection.SelectedOptionID
    INNER JOIN dbo.DropDown ON dbo.DropDown.ID = dbo.DropDownSelection.DropDownID

)
SELECT E_ID, E_Type,
    P_ID, P_Name, P_DataType, P_Required, P_OnlyOne,
    PV_ID, PV_Value, PV_EntityID, PV_ValueEntityID,
    PV_UnitValueID, PV_UnitID, PV_UnitName, PV_UnitDesc, PV_MeasureID, PV_MeasureName, PV_UnitValue,
    PV_SelectionID, PV_DropDownID, PV_DropDownName, PV_DropDownOptionID, PV_DropDownOptionName, PV_DropDownOptionDesc,
    RecursiveLevel
FROM Entities
INNER JOIN [dbo].[Entity] AS dE
    ON dE.ID = PV_EntityID

The problem is the second query, the "recursive one" is getting the data I expect since I can't do the LEFT JOINs like in the first query. (At least to my understanding).

If I remove the fetching of the data that requires the LEFT (Outer) JOINs then the recursion works perfectly. My problem is I need both. Is there a way I can accomplish this?

Answer 1

Per http://msdn.microsoft.com/en-us/library/ms175972.aspx you can not have a left/right/outer join in a recursive CTE.

For a recursive CTE you can't use a subquery either so I sugest following this example.

They use two CTE's. The first is not recursive and does the left join to get the data it needs. The second CTE is recursive and inner joins on the first CTE. Since CTE1 is not recursive it can left join and supply default values for the missing rows and is guarenteed to work in the inner join.

However, you can also duplicate a left join with a union and subselect though it isn't really useful normally but it is interesting.

In that case, you would keep your first statement how it is. It will match all rows that join successfully.

Then UNION that query with another query that removes the join, but has a

NOT EXISTS(SELECT 1 FROM MISSING_ROWS_TABLE WHERE MAIN_TABLE.JOIN_CONDITION = MISSING_ROWS_TABLE.JOIN_CONDITION)

This gets all the rows that failed the previous join condition in query 1. You can replace the colmuns you would get from MISSING_ROWS_TABLE with NULL. I had to do this once using a coding framework that didn't support outer joins. Since recursive CTE's don't allow subqueries you have to use the first solution.