Nested while loop in SQL Server is not showing the expected result

Question

I am trying to connect records from two different tables so I can display the data in a tabular format in an SSRS tablix.

The code below does not return the expected results.

As is, for each item in Temp_A the loop updates everything with the last item in Temp_C. Here is the code:

CREATE TABLE #Temp_A
(
    [ID] INT,
    [Name] VARCHAR(255)
)

INSERT INTO #Temp_A ([ID], [Name]) 
VALUES (1, 'A'), (2, 'B')

CREATE TABLE #Temp_C
(
    [ID] INT,
    [Name] VARCHAR(255)
)

INSERT INTO #Temp_C ([ID], [Name]) 
VALUES (1, 'C'), (2, 'D')

CREATE TABLE #Temp_Main
(
    [Temp_A_ID] INT,
    [Temp_A_Name] VARCHAR(255),
    [Temp_C_ID] INT,
    [Temp_C_Name] VARCHAR(255),
)

DECLARE @MIN_AID int = (SELECT MIN(ID) FROM #Temp_A)
DECLARE @MAX_AID int = (SELECT MAX(ID) FROM #Temp_A)

DECLARE @MIN_DID int = (SELECT MIN(ID) FROM #Temp_C)
DECLARE @MAX_DID int = (SELECT MAX(ID) FROM #Temp_C)

WHILE @MIN_AID <= @MAX_AID
BEGIN
    WHILE @MIN_DID <= @MAX_DID
    BEGIN       
        INSERT INTO #Temp_Main([Temp_A_ID], [Temp_A_Name])
            SELECT ID, [Name]
            FROM #Temp_A 
            WHERE ID = @MIN_AID

        UPDATE #Temp_Main
        SET [Temp_C_ID] = ID, [Temp_C_Name] = [Name]
        FROM #Temp_C
        WHERE ID = @MIN_DID

        SET @MIN_DID = @MIN_DID + 1     
    END             

    SET @MIN_AID = @MIN_AID + 1 
    SET @MIN_DID = 1
END 

SELECT * FROM #Temp_Main

DROP TABLE #Temp_A
DROP TABLE #Temp_C
DROP TABLE #Temp_Main

Incorrect result:

Temp_A_ID | Temp_A_Name | Temp_C_ID | Temp_C_Name
----------+-------------+-----------+---------------
1           A             2           D
1           A             2           D
2           B             2           D
2           B             2           D

Expected results:

Temp_A_ID | Temp_A_Name | Temp_C_ID | Temp_C_Name
----------+-------------+-----------+---------------
1           A             1           C
1           A             2           D
2           B             1           C
2           B             2           D

What am I missing?

Gordon Linoff · Accepted Answer · 2019-06-11 19:41:33Z

2

You seem to want a cross join:

select a.*, c.*
from #Temp_A a cross join
     #Temp_C c
order by a.id, c.id;

Here is a db<>fiddle.

There is no need to write a WHILE loop to do this.

You can use insert to insert this into #TempMain, but I don't se a need to have a temporary table for storing the results of this query.

answered Jun 11, 2019 at 19:41

Gordon Linoff

1.3m62 gold badges705 silver badges857 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Victor_Tlepshev Over a year ago

I used a temp table because I have to update more columns.I just could figure out this first step. Thank you so much.

Collectives™ on Stack Overflow

Nested while loop in SQL Server is not showing the expected result

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related