Calculate a SUM across two tables

One of my customers called me in a panic last night.  They are a prop trader based in Chicago, and the bulk of their data is the trades that they execute throughout the day. Well, Friday was a pretty crazy day in the market -- stocks rose very high after the government's 2nd quarter growth estimate. Unfortunately, their systems queued up crazy, and they had to do a lot of manual adjustments post trade.  Not uncommon, and also not very fun.  

Anyway, because they struggled to handle the data-flow, they had to split their traffic into two target tables.  This was good intraday, because they got to trade all the way to the close.  At the end of the day, however, they needed one volume count -- not two.

That's all this is.  I've used their problem as an example.  This is just quick means to calculate a SUM across two tables. 

   -- Trader table, so we can translate the trdID

   CREATE TABLE dbo.Trader (

     trdID INT IDENTITY (1,1),

     trdName VARCHAR(25),

     trdDesk VARCHAR(25)

   )

   SET IDENTITY_INSERT dbo.Trader ON

   INSERT dbo.Trader (trdID,trdName,trdDesk)

   SELECT 1, 'John Doe','Equities'

   UNION

   SELECT 12, 'Edgar Smith','Forex'

   UNION

   SELECT 207, 'Jane Peters','Fixed Income'

   UNION

   SELECT 208, 'Jack Black','Futures'

   -- Their 1st trade table

   CREATE TABLE #table1 (trdDate DATE,trdID INT,Volume BIGINT)

   INSERT #table1 (trdDate,trdID,Volume)

   SELECT '9/26/2014',12,18005

   UNION

   SELECT '9/26/2014',1,100

   UNION

   SELECT '9/26/2014',207,12500

   UNION

   SELECT '9/26/2014',208,750

   -- Their 2nd trade table

   CREATE TABLE #table2 (trdDate DATE,trdID INT,Volume BIGINT)

   INSERT #table2 (trdDate,trdID,Volume)

   SELECT '9/26/2014',12,100

   UNION

   SELECT '9/26/2014',1,5500

   UNION

   SELECT '9/26/2014',207,1000

   UNION

   SELECT '9/26/2014',208,0

-- See data from both tables

SELECT * FROM #table1

SELECT * FROM #table2

      -- results

   trdDate        trdID    Volume

   2014-09-26 1 100

   2014-09-26 12 18005

   2014-09-26 207     12500

   2014-09-26 208 750

   trdDate        trdID    Volume

   2014-09-26 1 5500

   2014-09-26 12         100

   2014-09-26 207 1000

   2014-09-26 208 0

   -- Now we'll pull it all back out in one result-set, with the volumes summed

   SELECT trdDate,Trader,SUM(Volume) [Vol Traded]

   FROM

   (

       SELECT t1.trdDate,t2.trdName [Trader],t1.Volume

       FROM #table1 t1 INNER JOIN dbo.Trader t2

         ON t1.trdID = t2.trdID

       UNION ALL

       SELECT t1.trdDate,t2.trdName [Trader],t1.Volume

       FROM #table2 t1 INNER JOIN dbo.Trader t2

     ON t1.trdID = t2.trdID

   ) t

   GROUP BY trdDate,Trader

   ORDER BY trdDate,Trader

Our final result-set, volumes from both tables were summed into a single 'Vol Traded' --

   trdDate         Trader          Vol Traded

   2014-09-26    Edgar Smith        18105

   2014-09-26    Jack Black           750

   2014-09-26    Jane Peters        13500

   2014-09-26    John Doe            5600