How do I check if a SQL Server text column is empt

问题:

I am using SQL Server 2005. I have a table with a text column and I have many rows in the table where the value of this column is not null, but it is empty. Trying to compare against '' yields this response:

The data types text and varchar are incompatible in the not equal to operator.

Is there a special function to determine whether the value of a text column is not null but empty?

回答1:

where datalength(mytextfield)=0

回答2:

ISNULL(
case textcolum1
    WHEN '' THEN NULL
    ELSE textcolum1
END 
,textcolum2) textcolum1

回答3:

Actually, you just have to use the LIKE operator.

SELECT * FROM mytable WHERE mytextfield LIKE ''

回答4:

To get only empty values (and not null values):

SELECT * FROM myTable WHERE myColumn = ''

To get both null and empty values:

SELECT * FROM myTable WHERE myColumn IS NULL OR myColumn = ''

To get only null values:

SELECT * FROM myTable WHERE myColumn IS NULL

To get values other than null and empty:

SELECT * FROM myTable WHERE myColumn <> ''

And remember use LIKE phrases only when necessary because they will degrade performance compared to other types of searches.

回答5:

You could do like

SELECT * FROM TABLE WHERE FIELDNAME=''

回答6:

I know this post is ancient but, I found it useful.

It didn't resolve my issue of returning the record with a non empty text field so I thought I would add my solution.

This is the where clause that worked for me.

WHERE xyz LIKE CAST('% %' as text)

回答7:

Use the IS NULL operator:

Select * from tb_Employee where ename is null

回答8:

I would test against SUBSTRING(textColumn, 0, 1)

回答9:

Are null and an empty string equivalent? If they are, I would include logic in my application (or maybe a trigger if the app is "out-of-the-box"?) to force the field to be either null or '', but not the other. If you went with '', then you could set the column to NOT NULL as well. Just a data-cleanliness thing.

回答10:

I wanted to have a predefined text("No Labs Available") to be displayed if the value was null or empty and my friend helped me with this:

StrengthInfo = CASE WHEN ((SELECT COUNT(UnitsOrdered) FROM [Data_Sub_orders].[dbo].[Snappy_Orders_Sub] WHERE IdPatient = @PatientId and IdDrugService = 226)> 0)
                            THEN cast((S.UnitsOrdered) as varchar(50))
                    ELSE 'No Labs Available'
                    END

回答11:

You have to do both:

SELECT * FROM Table WHERE Text IS NULL or Text LIKE ''

回答12:

I know there are plenty answers with alternatives to this problem, but I just would like to put together what I found as the best solution by @Eric Z Beard & @Tim Cooper with @Enrique Garcia & @Uli Köhler.

If needed to deal with the fact that space-only could be the same as empty in your use-case scenario, because the query below will return 1, not 0.

SELECT datalength(' ')

Therefore, I would go for something like:

SELECT datalength(RTRIM(LTRIM(ISNULL([TextColumn], ''))))

回答13:

Use DATALENGTH method, for example:

SELECT length = DATALENGTH(myField)
FROM myTABLE

回答14:

SELECT * FROM TABLE
WHERE ISNULL(FIELD, '')=''

回答15:

try this:

select * from mytable where convert(varchar, mycolumn) = ''

i hope help u!