如何用空字符串替换空字段值？

Question

我需要用空白字符串替换“估计数字”字段中的空值。我已经尝试了下面的代码，但值仍然显示为 null。有什么想法吗？谢谢

Pro Number      Estimate Number

10271943        NULL
10271944        NULL
10271945        NULL
10271946        NULL
10271948        94606


SELECT a.AAAREFNUMVALUE AS "Pro Number",
    (SELECT TOP 1 isnull(a2.AAAREFNUMVALUE,'') 
    FROM dbo.AAATOREFNUMS a2
    WHERE a2.AAATRANSPORTTABLE  = a.AAATRANSPORTTABLE  AND 
    a2.AAAREFNUMTYPE = 4 
    ORDER BY a2.AAAREFNUMVALUE
    ) AS "Estimate Number"

FROM dbo.AAATOREFNUMS a 
INNER JOIN dbo.AAATODATES d ON a.AAATRANSPORTTABLE = d.AAATRANSPORTTABLE

WHERE a.AAAREFNUMTYPE = 1 AND d.AAADATETYPE = 1  
GROUP BY a.AAAREFNUMVALUE,a.AAATRANSPORTTABLE,a.AAAREFNUMTYPE;

Answer 1

当子查询returns没有值时出现问题。 isnull() 需要在子查询之外：

ISNULL( (SELECT TOP 1 a2.AAAREFNUMVALUE
         FROM dbo.AAATOREFNUMS a2
         WHERE a2.AAATRANSPORTTABLE  = a.AAATRANSPORTTABLE  AND 
               a2.AAAREFNUMTYPE = 4 
         ORDER BY a2.AAAREFNUMVALUE
        ), ''
      ) AS "Estimate Number"

请注意，在这种情况下，ISNULL() 优于 COALESCE()，因为 COALESCE() 的 SQL 服务器实现对第一个参数求值两次，而实际上它不是NULL.

但是，如果您改用 window 函数，您可能会发现查询更容易表达并且更快运行：

SELECT DISTINCT a.AAAREFNUMVALUE AS "Pro Number",
       COALESCE(a.AAAREFNUMVALUE_4, '') as "Estimate Number"
FROM (SELECT a.*,
             MAX(CASE WHEN a.AAAREFNUMTYPE = 4 THEN a.AAAREFNUMVALUE END) OVER (PARTITION BY a.AAATRANSPORTTABLE) as AAAREFNUMVALUE_4
      FROM dbo.AAATOREFNUMS a
     ) a INNER JOIN
     dbo.AAATODATES d
     ON a.AAATRANSPORTTABLE = d.AAATRANSPORTTABLE
WHERE a.AAAREFNUMTYPE = 1 AND d.AAADATETYPE = 1  ;

Answer 2

试用案例，调整一下：

CASE 
(SELECT TOP 1 a2.AAAREFNUMVALUE
    FROM dbo.AAATOREFNUMS a2
    WHERE a2.AAATRANSPORTTABLE  = a.AAATRANSPORTTABLE  AND 
    a2.AAAREFNUMTYPE = 4 
    ORDER BY a2.AAAREFNUMVALUE) as Estimate Number
  WHEN NULL THEN ''
  ELSE 
    a2.AAAREFNUMVALUE
END as "Estimate Number"

Answer 3

你可以试试这个。

SELECT a.AAAREFNUMVALUE AS "Pro Number",
    ISNULL((SELECT TOP 1 isnull(a2.AAAREFNUMVALUE,'') 
    FROM dbo.AAATOREFNUMS a2
    WHERE a2.AAATRANSPORTTABLE  = a.AAATRANSPORTTABLE  AND 
    a2.AAAREFNUMTYPE = 4 
    ORDER BY a2.AAAREFNUMVALUE
    ),'') AS "Estimate Number"

FROM dbo.AAATOREFNUMS a 
INNER JOIN dbo.AAATODATES d ON a.AAATRANSPORTTABLE = d.AAATRANSPORTTABLE

WHERE a.AAAREFNUMTYPE = 1 AND d.AAADATETYPE = 1  
GROUP BY a.AAAREFNUMVALUE,a.AAATRANSPORTTABLE,a.AAAREFNUMTYPE;

如何用空字符串替换空字段值？

How to replace null field values with an empty string?

sql

sql-server

ssms