在MSSQL Server的不同列中的计算中使用一列结果

Question

I'm trying to use the result from one column in computation in later columns in MS SQL Server.

Below is my SQL code:

SELECT 
(SELECT 'EURUSD' AS a) AS symbol_name,
(SELECT TOP 1  ROUND(p.BidLast,5) FROM mt5_prices p WHERE p.Symbol LIKE 'EURUSD%') AS Bid,

(SELECT SUM(m.Volume) 
FROM mt5_positions m
WHERE m.Symbol LIKE 'EURUSD%' AND m.Login IN (SELECT u.Login FROM mt5_users u WHERE u."Group" LIKE 'real%') AND m."Action" = 0) AS TotalBuy,

(SELECT CASE 
WHEN 'EURUSD' LIKE 'USOIL%' OR 'EURUSD' LIKE 'UKOIL%' OR 'EURUSD' LIKE 'Bund%' THEN ROUND(TotalBuy/10*Bid,2) 
WHEN 'EURUSD' LIKE 'NGAS%' OR 'EURUSD' LIKE 'Copper%' THEN ROUND(TotalBuy/1*Bid,2)
ELSE ROUND(TotalBuy/100*Bid,2) END) AS ExpositionBuyLots

Of course, the error returned is:

SQL Error (207): Invalid column name 'TotalBuy'
Invalid column name 'Bid'.

My question is: How can I use the already (or, so to speak "on-the-fly") computed result from columns TotalBuy and Bid ? I read about computed columns, but unfortunately, modification of database is not possible.

MS SQL Server 2012 version.

EDIT: The above functionality is available in MySQL, I hope in MS SQL this can be achieved too. If someone is interested about the solution (I chose @Damien because it is closest one to the original MySQL query (yes, it is query, rewritten from MySQL to MSSQL), ie require only small SQL modification):

SELECT * FROM    
(SELECT 'EURUSD' AS symbol_name) symbol_name

CROSS apply

(SELECT TOP 1  ROUND(p.AskLast,5) AS Ask FROM mt5_prices p WHERE p.Symbol LIKE 'EURUSD%') Ask

CROSS apply

(SELECT TOP 1  ROUND(p.BidLast,5) AS Bid FROM mt5_prices p WHERE p.Symbol LIKE 'EURUSD%') Bid

CROSS apply

(SELECT SUM(m.Volume) AS TotalBuy
FROM mt5_positions m
WHERE m.Symbol LIKE 'EURUSD%' AND m.Login IN (SELECT u.Login FROM mt5_users u WHERE u."Group" LIKE 'real%') AND m."Action" = 0) TotalBuy

CROSS apply

(SELECT SUM(m.Volume) AS TotalSell
FROM mt5_positions m
WHERE m.Symbol LIKE 'EURUSD%' AND m.Login IN (SELECT u.Login FROM mt5_users u WHERE u."Group" LIKE 'real%') AND m."Action" = 1) TotalSell

CROSS apply

(SELECT (CASE 
WHEN 'EURUSD' LIKE 'USOIL%' OR 'EURUSD' LIKE 'UKOIL%' OR 'EURUSD' LIKE 'Bund%' THEN ROUND(TotalBuy/10*Bid,2) 
WHEN 'EURUSD' LIKE 'NGAS%' OR 'EURUSD' LIKE 'Copper%' THEN ROUND(TotalBuy/1*Bid,2)
ELSE ROUND(TotalBuy/100*Bid,2) END) AS ExpositionBuyLots) ExpositionBuyLots

Answer 1

You can use another sub query block to achieve this:

SELECT (
        CASE 
            WHEN 'EURUSD' LIKE 'USOIL%'
                OR 'EURUSD' LIKE 'UKOIL%'
                OR 'EURUSD' LIKE 'Bund%'
                THEN ROUND(TotalBuy / 10 * Bid, 2)
            WHEN 'EURUSD' LIKE 'NGAS%'
                OR 'EURUSD' LIKE 'Copper%'
                THEN ROUND(TotalBuy / 1 * Bid, 2)
            ELSE ROUND(TotalBuy / 100 * Bid, 2)
            END
        ) AS ExpositionBuyLots, *
FROM (
    SELECT ( SELECT 'EURUSD' AS a ) AS symbol_name
          ,( SELECT TOP 1 ROUND(p.BidLast, 5)
            FROM mt5_prices p
            WHERE p.Symbol LIKE 'EURUSD%'
            ) AS Bid
          ,( SELECT SUM(m.Volume)
            FROM mt5_positions m
            WHERE m.Symbol LIKE 'EURUSD%'
                AND m.LOGIN IN (
                    SELECT u.LOGIN
                    FROM mt5_users u
                    WHERE u."Group" LIKE 'real%'
                    )
                AND m."Action" = 0
            ) AS TotalBuy
    ) AS R

Answer 2

You can use cross apply (or subqueries) to introduce additional select clauses. Each select clause is computed "as if" all expressions are computed in parallel - that's why there cannot be dependencies between the expressions within a single select clause.

Eg:

select
    *
from
    sys.objects
        cross apply
    (select object_id + 10 as mega_object_id) u
        cross apply
    (select mega_object_id / 30 as little_object_id) w

Answer 3

You should use APPLY operator. You can use values from YourTable in APPLY

SELECT 
    ExpositionBuyLots = CASE 
        WHEN 'EURUSD' LIKE 'USOIL%' OR 'EURUSD' LIKE 'UKOIL%' OR 'EURUSD' LIKE 'Bund%' THEN ROUND(ComputedValues.TotalBuy/10*ComputedValues.Bid,2) 
        WHEN 'EURUSD' LIKE 'NGAS%' OR 'EURUSD' LIKE 'Copper%' THEN ROUND(ComputedValues.TotalBuy/1*ComputedValues.Bid,2)
        ELSE ROUND(ComputedValues.TotalBuy/100 * ComputedValues.Bid,2) END
FROM YourTable
OUTER APPLY (
    SELECT
        symbol_name = 'EURUSD',
        Bid         = (SELECT TOP 1  ROUND(p.BidLast,5) FROM mt5_prices p WHERE p.Symbol LIKE 'EURUSD%') ,
        TotalBuy    = (SELECT SUM(m.Volume) 
                          FROM mt5_positions m
                          WHERE m.Symbol LIKE 'EURUSD%' AND m.Login IN (SELECT u.Login FROM mt5_users u WHERE u."Group" LIKE 'real%') AND m."Action" = 0
                      ) 
) ComputedValues