sql - WHERE/AND 句で変数に値を代入する

Question

クエリの AND ステートメントで 3 回リストする必要があるかなり大きな SQL 式を扱っています。読みやすさを向上させるために、式を変数に設定し、それを 3 回参照するだけにします。しかし、私はこれを進めるのに苦労しています。たとえば、BEGIN SET … END を試してみましたが、BEGIN ブロックには無効な場所のようです。最上位のクエリ項目 (LowPrice) も参照しようとしましたが、認識されませんでした。

クエリは次のとおりです。

SELECT cl.claimid, cl.GUID1 AS [GUID1], cl.GUID2 AS [GUID2]
    ,cs.Conclusion AS [ClaimStatus]
    ,CASE [Type] WHEN 0 THEN 'a' + REPLACE(STR(Precedence,5),' ','0') ELSE 'b' + REPLACE(STR(Precedence,5),' ','0') END TransactionNumber
    ,tr.TradeDate AS [TradeDate]
    ,REPLACE(CONVERT(varchar(16),cast(Shares as money),1), ',', '') AS [Shares]
    ,tr.PricePerShare AS [Price]
    ,CASE WHEN tr.Custom IS NULL THEN '' ELSE tr.Custom END AS [ML]
    ,ISNULL((SELECT TOP 1 LowPrice FROM ca_historical_sec h 
        WHERE caseId = @caseid AND [Security] = 'Common Stock' AND h.TradeDate = tr.TradeDate
        ORDER BY tradeDate DESC),0) AS LowPrice
    ,ISNULL((SELECT TOP 1 HighPrice FROM ca_historical_sec h 
        WHERE caseId = @caseid AND [Security] = 'Common Stock' AND h.TradeDate = tr.TradeDate 
        ORDER BY tradeDate DESC),0) AS HighPrice
    ,CASE HasProof WHEN 1 THEN 'HAS PROOF' ELSE 'NO PROOF' END HasProof
FROM ca_claim cl
CROSS APPLY (
                --Get all fields of the top row
                SELECT TOP 100 PERCENT *
                FROM ca_transaction_sec tr 
                WHERE tr.claimId  = cl.claimid
                AND tr.type < 2
                AND (PricePerShare > 0 AND PricePerShare NOT BETWEEN
                     (
--- Trying to do it here ----
                      --BEGIN SET @ThePrice = ISNULL((SELECT TOP 1 LowPrice FROM ca_historical_sec h WHERE caseId = @caseid AND h.tradeDate = tr.tradeDate AND [Security] = 'Common Stock' ORDER BY h.tradeDate DESC),0) END
                      CASE WHEN @MarginType = 'Percent' THEN ISNULL((SELECT TOP 1 LowPrice FROM ca_historical_sec h WHERE caseId = @caseid AND h.tradeDate = tr.tradeDate AND [Security] = 'Common Stock' ORDER BY h.tradeDate DESC),0) - (ISNULL((SELECT TOP 1 LowPrice FROM ca_historical_sec h WHERE caseId = @caseid AND h.tradeDate = tr.tradeDate AND [Security] = 'Common Stock' ORDER BY h.tradeDate DESC),0) * @percentMargin)
                      ELSE ISNULL((SELECT TOP 1 LowPrice FROM ca_historical_sec h WHERE caseId = @caseid AND h.tradeDate = tr.tradeDate AND [Security] = 'Common Stock' ORDER BY h.tradeDate DESC),0) - @dollarMargin END
                     )
                     AND 
                     (
                      --Ideally this would be something like:
                      BEGIN SET @HighPrice = .... END
                      CASE WHEN @MarginType = 'Percent' THEN @HighPrice + (@HighPrice * @percentMargin)
                      ELSE @HighPrice + @dollarMargin END
                     )
                    )
                AND (@caseid <> 177 
                    OR (@caseid = 177 AND 0 = 0 AND ISNULL(tr.custom,'') in ('',' ','D')) 
                    OR (@caseid = 177 AND 0 = 1 AND tr.custom = 'A')) 
                order by tr.createdon
            ) tr
LEFT OUTER JOIN ca_ClaimStatus cs ON cl.claimid = cs.claimid
WHERE cl.caseId = @caseid

ご覧のとおり、ISNULL((SELECT TOP 1 LowPrice FROM ca_historical_sec h WHERE caseId = @caseid AND h.tradeDate = tr.tradeDate AND [Security] = 'Common Stock' ORDER BY h.tradeDate DESC),0)は非常に長い式です。また、CROSS APPLY の前にクエリ項目の 1 つとして既にリストされています。その値に等しい変数を設定したいと思います。CROSS APPLYを維持しながらこれを行う方法はありますか?