1

I'm not used to querying text columns with a large amount of data as I've always used NVARCHAR(MAX) and VARCHAR(MAX) but this is not my Database that I'm querying.

myTable has 305,000 rows.

myDescriptionField is a text column and allows nulls & has loads of data in it.

When I run the following query, it returns a row instantly.

SELECT TOP 1 userid
FROM myTable 
WHERE ISNULL(userID,0) > 0 
AND TRIM(SUBSTRING(myDescriptionField,1,1)) is not null

However, when I add this line to the where clause, the query just sits for over a minute (not sure how long it actually takes to finish as I always end up stopping the execution).

AND myDescriptionField NOT LIKE ''

I thought it might be because I'm forced to do a not like as it's a text column and also that it may be where a lot of rows have blanks or null so I tried different combinations of the following :-

AND ISNULL(TRIM(SUBSTRING(myDescriptionField,1,1)),'') <> ''

None of this worked.

So now a quick explanation as to what I need to achieve :-

I just need to find out if at least one row has data in the column myDescriptionField and if so, I can move on to the next table.

Is there a quick way of returning just one row once it's hit one?

  • Can you use LEN? - where len(TRIM(SUBSTRING(myDescriptionField,1,1))) > 0 – Scott Hodgin Jun 6 '18 at 15:18
  • Tried LEN > 0 but still no joy. – J.B. Jun 6 '18 at 15:22
  • I can't alter the table as it's not my database. – J.B. Jun 6 '18 at 15:22
  • Nope. Still no good. Also, isn't my SUBSTRING basically converting it to VARCHAR anyway? – J.B. Jun 6 '18 at 15:36
1

Can you use DATALENGTH?

SELECT TOP 1
    userID
FROM
    myTable 
WHERE
    DATALENGTH(myDescriptionField) >= 1
  • This could be the answer. Thanks. I'll just run some test and let you know if it's solved my problem. – J.B. Jun 6 '18 at 15:46
1

Not sure if you added another predicate, or if you changed the existing one, but you could try like:

SELECT TOP 1 userid
FROM myTable 
WHERE ISNULL(userID,0) > 0 
  AND NULLIF(SUBSTRING(myDescriptionField,1,1),'') is not null;
  • Yes. I did try this but of course it doesn't work because it's a Text field and it returns the following error :- The data types text and varchar are incompatible in the equal to operator. – J.B. Jun 6 '18 at 14:56
  • Totally agree with you. I only added the Trim bit out of desperation and after reading someone else's suggestion on the net. However, taking that out has no affect on the performance. – J.B. Jun 6 '18 at 15:00
  • I see, so you are using substring to cast text to varchar? I'll update my answer – Lennart Jun 6 '18 at 15:00
  • Exactly. As mentioned in my original question, I'm not used to handling Text fields so if there's a better way of doing this I'd be interested. Thanks for your help so far by the way. Also, the substring was an attempt to look at less data. – J.B. Jun 6 '18 at 15:04
  • Still not working unfortunately. – J.B. Jun 6 '18 at 15:16

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