Question

I want to know if I can add a join in to a SQL statement based on a an IF statement. I’ve got a query with three variables and I only want to include the join if the third variable is actually filled in. This is my query:

-- Returns all new woksteps for a given time period
-- Includes the ability to narrow down to a specific arrangment

DECLARE @start_added_date DATETIME
DECLARE @end_added_date DATETIME
DECLARE @arrang_part_key INT

SET @start_added_date = '1/4/2011'
SET @end_added_date = '1/5/2011'
SET @arrang_part_key = '1230631'

-- Compensate for CST in the database
SET @end_added_date = DATEADD(DAY, 1, @end_added_date)

SELECT DISTINCT
  PWS.Part_Work_Step_Key,
  O.Operation_Code,
  WS.Work_Step,
  PWS.Sort_Order,
  U.User_ID,
  PWS.Added_Date,
  PWS.Cycle_Time,
  ET.ECR_Type,
  E.ECR_No,
  PWS.Effective_Date,
  P.Part_No,
  P.Revision,
  P.Name
FROM Part_V_Part_Work_Step PWS
JOIN Part_V_Work_Step WS
  ON WS.Work_Step_Key = PWS.Work_Step_Key
JOIN Part_V_Operation O
  ON O.Operation_Key = PWS.Operation_Key
JOIN User U
  ON U.User_No = PWS.Added_By
JOIN Part_V_ECR E
  ON E.ECR_Key = PWS.Effective_ECR_Key
JOIN Part_V_ECR_Type ET
  ON E.ECR_Type_Key = ET.ECR_Type_Key
JOIN Part_V_Part_Work_Step_BOM PWSB
  ON PWSB.Part_Work_Step_Key = PWS.Part_Work_Step_Key
JOIN Part_V_BOM B
  ON B.BOM_Key = PWSB.BOM_Key
JOIN Part_V_Part P
  ON P.Part_Key = B.Part_Key

IF @arrang_part_key IS NOT NULL
BEGIN
JOIN 
(
    SELECT
      AGP.Part_Key
    FROM Part_V_Flat_BOM FB
    JOIN Part_V_Part AGP
      ON AGP.Part_Key = FB.Component_Part_Key
    JOIN Part_V_Part_Group PG
      ON AGP.Part_Group_Key = PG.Part_Group_Key
     AND PG.Part_Group = 'Engineering Group'
    WHERE FB.Part_Key = @arrang_part_key
) AG
  ON AG.Part_Key = P.Part_Key
END

WHERE PWS.Part_Key IS NULL
  AND PWS.Added_Date BETWEEN @start_added_date AND @end_added_date
  AND PWS.Active = 1

ORDER BY
  O.Operation_Code,
  PWS.Sort_Order

But when I run the query I get this as my result:

Error: Incorrect syntax near the keyword 'JOIN'
Error: Incorrect syntax near 'AG'

I am beginning to think that this isn’t the right approach to solving my problem. The query is trying to kill two birds with one stone, return all results for a given time frame, and then allow for filtering down to a specific arrangement if supplied.

Answer 1

OK, so adding a join by an IF block simply cannot work. But I’ve found a way to do my query as well as utilize as much re-usable code as I could think of.

There were two key elements to the query:

1. Query the work step table all the time
2. Filter by an arrangement occasionally

To accomplish this I used a combination of both a Table Variable and a CTE (Common Table Expression) and then placed two queries in to my if..else block.

The new query looks like this:

-- Returns all new woksteps for a given time period
-- Includes the ability to narrow down to a specific arrangment

DECLARE @start_added_date DATETIME
DECLARE @end_added_date DATETIME
DECLARE @arrang_part_key INT

SET @start_added_date = '1/4/2011'
SET @end_added_date = '1/5/2011'
SET @arrang_part_key = '1230631'
--SET @arrang_part_key = NULL

-- Compensate for CST in the database
SET @end_added_date = DATEADD(DAY, 1, @end_added_date)

DECLARE @Work_Step_Table TABLE
(
  Customer_Number INT,
  Part_Work_Step_Key INT,
  Operation_Code VARCHAR(255),
  Work_Step VARCHAR(255),
  Sort_Order INT,
  User_Id VARCHAR(255),
  Added_Date DATETIME,
  Cycle_Time Float,
  ECR_Type VARCHAR(255),
  ECR_No INT,
  Effective_Date DATETIME,
  Part_Key INT,
  Part_No VARCHAR(255),
  Revision VARCHAR(255),
  Name VARCHAR(255)
)

INSERT INTO @Work_Step_Table
SELECT DISTINCT
  P.Customer_Number,
  PWS.Part_Work_Step_Key,
  O.Operation_Code,
  WS.Work_Step,
  PWS.Sort_Order,
  U.User_ID,
  PWS.Added_Date,
  PWS.Cycle_Time,
  ET.ECR_Type,
  E.ECR_No,
  PWS.Effective_Date,
  P.Part_Key,
  P.Part_No,
  P.Revision,
  P.Name
FROM Part_V_Part_Work_Step PWS
JOIN Part_V_Work_Step WS
  ON WS.Work_Step_Key = PWS.Work_Step_Key
JOIN Part_V_Operation O
  ON O.Operation_Key = PWS.Operation_Key
JOIN User U
  ON U.User_No = PWS.Added_By
JOIN Part_V_ECR E
  ON E.ECR_Key = PWS.Effective_ECR_Key
JOIN Part_V_ECR_Type ET
  ON E.ECR_Type_Key = ET.ECR_Type_Key
JOIN Part_V_Part_Work_Step_BOM PWSB
  ON PWSB.Part_Work_Step_Key = PWS.Part_Work_Step_Key
JOIN Part_V_BOM B
  ON B.BOM_Key = PWSB.BOM_Key
JOIN Part_V_Part P
  ON P.Part_Key = B.Part_Key

WHERE PWS.Part_Key IS NULL
  AND PWS.Added_Date BETWEEN @start_added_date AND @end_added_date
  AND PWS.Active = 1


IF (@arrang_part_key > 0)
BEGIN 
;WITH Arrangement_Groups (PCN, Arrangement_Part_Key, Component_Part_Key) AS
(
    SELECT
      AGP.Customer_Number,
      FB.Part_Key AS Arrangement_Part_Key,
      AGP.Part_Key AS Component_Part_Key      
    FROM Part_V_Flat_BOM FB
    JOIN Part_V_Part AGP
      ON AGP.Part_Key = FB.Component_Part_Key
    JOIN Part_V_Part_Group PG
      ON AGP.Part_Group_Key = PG.Part_Group_Key
     AND PG.Part_Group = 'Engineering Group'
    WHERE FB.Part_Key = @arrang_part_key
)
SELECT
  *
FROM @Work_Step_Table WST
JOIN Arrangement_Groups AG 
  ON AG.Component_Part_Key = WST.Part_Key  
ORDER BY
  WST.Operation_Code,
  WST.Sort_Order
END

ELSE
 BEGIN
  SELECT
    *
  FROM @Work_Step_Table WST
  ORDER BY
    WST.Operation_Code,
    WST.Sort_Order
 END

The table variable will always be created and populated with the relevant records for the date range. The IF..Else block will check for an additional arrangement key and create the additional CTE if needed and filter accordingly.