如果SQL查询在SQL中返回零值，如何将结果返回为NULL

Question

I have an sql query where I want to return the value as "NULL" if there is no result set after the query execution. I Have tried ISNULL property but, its generating an error,

my query is :

SELECT ISNULL((SELECT TOP (100) PERCENT a.ReportDate, a.Scripcode, a.ISIN, a.Scripname, a.AccountNo, a.ClientLongName, a.GroupName, a.Event, a.TradedQty, a.UnreconQty, a.ExDateQty, a.RecDateQty, a.Diff, a.Rate, a.Ratio, a.TotalValue, a.Shares, a.StartDate, a.ExDate, a.RecordDate, a.PayDate, a.AgmDate, a.NSecName, a.NSecNo, a.Remark, b.GRUL_PROX_GRP_ID, b.GRUL_GROUPNO, b.CUSTOMERNO, b.GRUL_SHORTNAME, b.GRUP_SHORTCODE, b.CONF_TYP, b.SWIFT, b.FAX, b.COURIER, b.EMAIL, b.Account_Group, b.Excel_Word, b.Password, b.Sub_Account_Flag 
FROM       dbo.CRS_Entitlement_MasterDate AS a 
INNER JOIN dbo.CRS_Entitlement_EntitlementComn AS b 
ON         a.AccountNo = b.CUSTOMERNO
WHERE      (b.Account_Group = 'A') 
AND        (b.Excel_Word = 'E') 
AND        (b.SWIFT <> 'v') 
AND        (b.CONF_TYP <> 'N/A') 
AND        (b.FAX = 'v') 
OR         (b.Account_Group = 'A') 
AND        (b.Excel_Word = 'E') 
AND        (b.SWIFT <> 'v') 
AND        (b.CONF_TYP <> 'N/A') 
AND        (b.COURIER = 'v') 
OR         (b.Account_Group = 'A') 
AND        (b.Excel_Word = 'E') 
AND        (b.SWIFT <> 'v') 
AND        (b.CONF_TYP <> 'N/A') 
AND        (b.EMAIL = 'v')
ORDER BY   a.AccountNo), 0) AS Expr1

please help me to solve this ,Thanks in Advance!!!

Answer 1

Use EXISTS like so:

-- returns NULL when it doesn't exist
SELECT  CASE WHEN EXISTS ( SELECT   1 AS val
                           WHERE    1 = 2 ) THEN 1
             ELSE NULL
        END RESULT;

-- returns something else, in this case 1 when it does exist    
SELECT  CASE WHEN EXISTS ( SELECT   1 AS val
                           WHERE    1 = 1 ) THEN 1
             ELSE NULL
        END RESULT;

EXISTS (Transact-SQL)

Specifies a subquery to test for the existence of rows.

A sample with data:

CREATE TABLE #test ( id INT );

INSERT  INTO #test
        ( id )
VALUES  ( 1 ),
        ( 2 ),
        ( 3 );

-- returns data
IF ( EXISTS ( SELECT    *
              FROM      #test
              WHERE     id > 0 ) )
    SELECT  *
    FROM    #test
    WHERE   id > 0;
ELSE
    SELECT  NULL;

 -- returns NULL 
 IF ( EXISTS ( SELECT    *
              FROM      #test
              WHERE     id > 5 ) )
    SELECT  *
    FROM    #test
    WHERE   id > 5;
ELSE
    SELECT  NULL AS Result;


DROP TABLE #test;     

Answer 2

您不能在内部查询中放置多个列。例如，选择top（100）％a.ReportDate ----将起作用