如果已包含數據，則不允許使用空值更新列

Question

我有一個數據源正在從中更新現有表。

只有當源數據不是NULL時，才更新每個字段中的值的方法？

Answer 1

你應該使用ISNULL(@paramA, ColumnA)：

UPDATE someTable 
set ColumnA = ISNULL(@ParamA, ColumnA) 
WHERE 
..... 

Answer 2

考慮到，美中提到，如果源數據不爲null，考慮然後更新

--Create a sample table 

DECLARE @SAMPLE TABLE 
(
SourceID INT IDENTITY(1,1), 
SourceData NVARCHAR(255) 
) 

--Create dummy data 

INSERT INTO @SAMPLE VALUES ('SOMETHING') 
INSERT INTO @SAMPLE VALUES (NULL) 
INSERT INTO @SAMPLE VALUES ('SOMETHING') 


--update source data that is not null, this will update entire table 

UPDATE @SAMPLE 
SET SourceData = 'New Data' 
FROM @SAMPLE t1 
INNER JOIN (
SELECT * FROM @SAMPLE Where SourceData is not null) t2 
ON t1.SourceID = t2.SourceID 

或者如果你只是想更新選定的記錄

--Pass in your variable 

DECLARE @SourceID INT 

--play around your source id 

SET @SourceID = 2 

--if the particular id is with null data, then update will never perform 

IF EXISTS(SELECT 1 FROM @SAMPLE WHERE SourceID = @SourceID and SourceData is not null) 
Update @SAMPLE 
set SourceData = 'New Item' 
where SourceID = @SourceID