How to dynamically do union operator and get records

See more:

SQL-Server-2014

Hi,
I have about 24 tables (JanSales13 – DecSales14) with exact the same columns for each month. I want to be able to join each of these tables dynamically or alternatively. That is to dynamically choose the tables (eg.FebSales13 & JulySales13 OR DecSales13 & AprilSales14 ). First of all I need to union the chosen /selected tables. After the union operator combines these tables, I want to select some columns and then aggregate their transactional data. The logic: To be able to choose any two tables. The tables should then combine into one. After the UNION operator, get record of the union table

That’s what I have so far. A dynamic union table. The user should be able to choose any table:

CREATE PROC spCombine
   @Table_Name  sysname,
   @Table_Name2  sysname
AS
BEGIN
  SET NOCOUNT OFF;

DECLARE @Dynamictbl nvarchar(MAX)

SET @Dynamictbl = 
N'SELECT * FROM ' + @Table_Name +
' UNION
SELECT * FROM ' + @Table_Name2

EXECUTE sp_executesql @Dynamictbl

END

But I want to also add a query within this store procedure to get records of the two combined tables

SELECT
 Product, Description,
 Sum(A_Sales ) AS [A_salesFeb],
 Sum(A_Sales ) AS [A_salesMay],
 Sum(A_Sales ) AS [B_salesFeb],
 Sum(A_Sales ) AS [B_salesMay],
 Sum(A_Sales ) AS [C_salesFeb],
 Sum(A_Sales ) AS [C_salesMay],
FROM ……
GROUP BY Product, Description

So my expectation is if I execute the store procedure, the below three steps take place

EXEC spCombine @Table_Name =’ FebSales13’, @Table_Name2=’ MaySales13’

1.Choose any two tables
2.Combine them together
3.Results from main query

image explaination:[^]