Question

我有这个问题：

SELECT        cod_commessa, (ISNULL(ccomm.costi, 0) + ISNULL(ccomm.imp_costi, 0) - ISNULL(ccomm.rid_costi, 0)) -
                             ((SELECT        ISNULL(costi, 0) AS Expr1
                                 FROM            t_costi_commesse AS tbs
                                 WHERE        (cod_commessa = ccomm.cod_commessa) AND (anno = YEAR(DATEADD(m, - 1, CAST(CAST(ccomm.anno AS varchar) + REPLICATE('0', 
                                                          2 - LEN(CAST(ccomm.mese AS varchar))) + CAST(ccomm.mese AS varchar) + '01' AS smalldatetime)))) AND (mese = MONTH(DATEADD(m, - 1, 
                                                          CAST(CAST(ccomm.anno AS varchar) + REPLICATE('0', 2 - LEN(CAST(ccomm.mese AS varchar))) + CAST(ccomm.mese AS varchar) 
                                                          + '01' AS smalldatetime))))) +
                             (SELECT        ISNULL(imp_costi, 0) AS Expr1
                               FROM            t_costi_commesse AS tbs
                               WHERE        (cod_commessa = ccomm.cod_commessa) AND (anno = YEAR(DATEADD(m, - 1, CAST(CAST(ccomm.anno AS varchar) + REPLICATE('0', 
                                                         2 - LEN(CAST(ccomm.mese AS varchar))) + CAST(ccomm.mese AS varchar) + '01' AS smalldatetime)))) AND (mese = MONTH(DATEADD(m, - 1, 
                                                         CAST(CAST(ccomm.anno AS varchar) + REPLICATE('0', 2 - LEN(CAST(ccomm.mese AS varchar))) + CAST(ccomm.mese AS varchar) 
                                                         + '01' AS smalldatetime))))) -
                             (SELECT        ISNULL(rid_costi, 0) AS Expr1
                               FROM            t_costi_commesse AS tbs
                               WHERE        (cod_commessa = ccomm.cod_commessa) AND (anno = YEAR(DATEADD(m, - 1, CAST(CAST(ccomm.anno AS varchar) + REPLICATE('0', 
                                                         2 - LEN(CAST(ccomm.mese AS varchar))) + CAST(ccomm.mese AS varchar) + '01' AS smalldatetime)))) AND (mese = MONTH(DATEADD(m, - 1, 
                                                         CAST(CAST(ccomm.anno AS varchar) + REPLICATE('0', 2 - LEN(CAST(ccomm.mese AS varchar))) + CAST(ccomm.mese AS varchar) 
                                                         + '01' AS smalldatetime)))))) AS 'costi'
                                                         FROM            t_costi_commesse AS ccomm INNER JOIN
                         t_commesse AS comm ON ccomm.cod_commessa = comm.codcema

此查询正确返回值，但有时我在列＆＃39; costi＆＃39;中有一些值。即使我将ISNULL应用于每个值，它仍然是NULL。奇怪的是，有时NULL值被正确地替换为0，但有时不会。

我还确定原始值为NULL（而不是字符串＆＃39; NULL＆＃39;），因为SQL Server Management Studio正确更改了背景颜色。

所以，我可以理解我的查询是否不正确，或者ISNULL因未知原因而无法正常工作。有什么建议吗？

Answer 1

将您在子查询中应用的ISNULL移至外部。

此：

select 1,(select object_id from sys.objects where 1=0)

产地：

1, NULL

尽管object_id不可以为空，但子查询不返回任何行。您无法在子查询的select中修复它，因为没有行。所以这个：

select 1,(select ISNULL(object_id,0) from sys.objects where 1=0)

没有解决问题但是：

select 1,ISNULL((select object_id from sys.objects where 1=0),0)

确实

ISNULL仍然返回NULL值

1 个答案: