有條件的聯盟T-SQL

Question

目前我有一個查詢，如下所示：

-- Query 1 
SELECT 
    acc_code, acc_name, alias, LAmt, coalesce(LAmt,0) AS amt 
FROM 
    (SELECT 
     acc_code, acc_name, alias, 
     (SELECT 
      (SUM(cr_amt)-SUM(dr_amt)) 
     FROM 
      ledger_mcg l 
     WHERE 
      (l.acc_code LIKE a.acc_code + '.%' OR l.acc_code=a.acc_code) 
     AND 
      fy_id=1 
     AND 
      posted_date BETWEEN '2010-01-01' AND '2011-06-02') AS LAmt 
    FROM 
     acc_head_mcg AS a 
    WHERE 
    (acc_type='4')) AS T1 
WHERE 
    coalesce(LAmt,0)<>0 

查詢2是相同的查詢1除了acc_type = '5'在查詢2.查詢2總是返回一個單行結果集。現在，我需要工會的兩個查詢，即

Query 1 
UNION 
Query 2 

只有當查詢2返回的AMT小於0。否則，我不需要從查詢工會，但只有resulset 1

我能想到的最好方法是創建一個參數化的標量函數。我該如何做到最好？

Answer 1

您可以將第一個查詢的結果存儲到一個臨時表中，如果該表不是空的，則執行另一個查詢。

IF OBJECT_ID('tempdb..#MultipleQueriesResults') IS NOT NULL 
    DROP TABLE #MultipleQueriesResults; 

SELECT 
    acc_code, acc_name, alias, LAmt, coalesce(LAmt,0) AS amt 
INTO #MultipleQueriesResults 
FROM 
    (SELECT 
     acc_code, acc_name, alias, 
     (SELECT 
      (SUM(cr_amt)-SUM(dr_amt)) 
     FROM 
      ledger_mcg l 
     WHERE 
      (l.acc_code LIKE a.acc_code + '.%' OR l.acc_code=a.acc_code) 
     AND 
      fy_id=1 
     AND 
      posted_date BETWEEN '2010-01-01' AND '2011-06-02') AS LAmt 
    FROM 
     acc_head_mcg AS a 
    WHERE 
    (acc_type='4')) AS T1 
WHERE 
    coalesce(LAmt,0)<>0; 

IF NOT EXISTS (SELECT * FROM #MultipleQueriesResults) 
    … /* run Query 2 */