March 17, 2020 at 1:08 pm
one of my colleagues asked me why this query doesn't do what he thinks it should
I ran a few tests and the blank spaces seem to be ignored
SELECT TOP (1000)
LEN(Area) length_of_area -- Should be 10, because there is a space at the end of Marketing
,*
,LEN(Area)
FROM [MyStore].[dbo].WebAreaAccess
WHERE AccountCode = 'marshorsecare'
AND Area LIKE '% %'
AND Area = 'Marketing ' -- This line and the next line should contradict each other
AND Area = 'Marketing' -- This line and the previous line should contradict each other
ORDER BY LEN(Area)
so - the blank spaces don't seem to be counted in the where clause - the 2 conflicting area statements surely should break each other..
I can put as many spaces as I want in the query and it still returns the same recordset
the field is a varchar(100) and collation is latin1 general ci as
anyone fancy educating me?
MVDBA
March 17, 2020 at 1:34 pm
I remembered coming across this article once upon a time which lead me here. If I recall correctly I was fighting with a similar sort of thing in a WHERE clause.
How to post a question to get the most help http://www.sqlservercentral.com/articles/Best+Practices/61537
March 17, 2020 at 1:35 pm
Spaces at the end of strings are usually ignored by SQL Server. Have a read here for some more detail.
--Neil beat me to it!
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.
March 17, 2020 at 4:48 pm
For varchar, LEN(Area) will give the trimmed length while DATALENGTH(Area) will give the actual length.
For nvarchar, LEN(Area) will give the trimmed length while DATALENGTH(Area) will give the actual length times two.
So for varchar DATALENGTH(Area) > LEN(Area) will show areas with trailing spaces.
March 17, 2020 at 5:39 pm
one of the ideas I looked at is reversing the string and checking the ascii value of the first character - please someone tell me that is a stupid idea
MVDBA
March 18, 2020 at 10:42 am
For varchar, LEN(Area) will give the trimmed length while DATALENGTH(Area) will give the actual length.
For nvarchar, LEN(Area) will give the trimmed length while DATALENGTH(Area) will give the actual length times two.
So for varchar DATALENGTH(Area) > LEN(Area) will show areas with trailing spaces.
I tried this and did some research - len and datalength gave the same value.
my understanding is that len gives you the number of characters, datalength gives you the number of bytes (since 1 char =1 byte then same thing) - datalength seems to be designed for the limitations of the size of field you can "len" - datalength can go much higher
MVDBA
March 18, 2020 at 11:05 am
SELECT LEN(Area + 'x') - 1
March 18, 2020 at 2:41 pm
The behaviour of DATALENGTH seems to depend on ANSI_PADDING when the table was created.
All my connections have ANSI_PADDING ON so I have never noticed the difference.
SET ANSI_PADDING ON;
IF SESSIONPROPERTY('ANSI_PADDING') = 1
PRINT 'ANSI_PADDING ON'
CREATE TABLE #tON
(
id int NOT NULL PRIMARY KEY
,Test varchar(20) NOT NULL
);
INSERT INTO #tON
VALUES(1,'test'),(2,'test '),(3,'test ');
SELECT *
,LEN(Test) AS LenTest
,DATALENGTH(Test) AS DataLengthTest
FROM #tON
SET ANSI_PADDING OFF;
IF SESSIONPROPERTY('ANSI_PADDING') = 0
PRINT 'ANSI_PADDING OFF'
CREATE TABLE #tOFF
(
id int NOT NULL PRIMARY KEY
,Test varchar(20) NOT NULL
);
INSERT INTO #tOFF
VALUES(1,'test'),(2,'test '),(3,'test ');
SELECT *
,LEN(Test) AS LenTest
,DATALENGTH(Test) AS DataLengthTest
FROM #tOFF
SET ANSI_PADDING ON;
March 18, 2020 at 2:50 pm
interesting - I had another comment that is was the session variable when the ROW was created rather than table creation. there is some "ambiguous" documentation around this area. (create/insert/select)
if it's a create table thing then I need to drop all tables and recreate, plus re-insert the old data...not a pleasant job
and if the correct ansi settings are on, will the BCP data conform? or will I have the same issues for legacy data?
MVDBA
March 18, 2020 at 3:15 pm
The following suggests it is the ANSI_PADDING setting with CREATE TABLE.
This is interesting. In future I think I am going to alter the first line of my CREATE TABLE scripts from:
SET ANSI_NULLS, QUOTED_IDENTIFIER ON;
to
SET ANSI_NULLS, QUOTED_IDENTIFIER, ANSI_PADDING ON;
SET ANSI_PADDING ON;
IF SESSIONPROPERTY('ANSI_PADDING') = 1
PRINT 'ANSI_PADDING ON'
CREATE TABLE #tON
(
id int NOT NULL PRIMARY KEY
,Test varchar(20) NOT NULL
);
INSERT INTO #tON VALUES (1,'test ');
GO
SET ANSI_PADDING OFF;
GO
INSERT INTO #tON VALUES (2,'test ');
SELECT *
,LEN(Test) AS LenTest
,DATALENGTH(Test) AS DataLengthTest
FROM #tON
SET ANSI_PADDING OFF;
IF SESSIONPROPERTY('ANSI_PADDING') = 0
PRINT 'ANSI_PADDING OFF'
CREATE TABLE #tOFF
(
id int NOT NULL PRIMARY KEY
,Test varchar(20) NOT NULL
);
INSERT INTO #tOFF VALUES (1,'test ');
GO
SET ANSI_PADDING ON;
GO
INSERT INTO #tOFF VALUES (2,'test ');
SELECT *
,LEN(Test) AS LenTest
,DATALENGTH(Test) AS DataLengthTest
FROM #tOFF
SET ANSI_PADDING ON;
March 18, 2020 at 3:19 pm
One of today's articles has a script to show columns created with ANSI_PADDING OFF
March 18, 2020 at 3:27 pm
There could be some ugly consequences in some cases if existing legacy data has trailing spaces contained in varchar data type columns, as both tables and indexes could get a difference in page splits (and any attendant nastiness) as a result of a change in the overall data length in a given row or set of rows that result from doing cleanup, such as RTRIM(column) being used as part of an INSERT statement. Mind you, we're talking about reducing the length of varchar data, but if done via copying a table into tempdb, and then inserting the smaller rows, the smaller row lengths now fit more rows in a page, and ya never know ahead of time what new kind of funky can occur when there's that kind of change, and especially when you already have existing page splits... You'd like to think that such might get better, but there's no assurance of that, and the more fragmented the available disk space within the MDF file is, the more likely that a problem can occur. I'd also not be surprised if an in-place UPDATE could cause similar issues.
Steve (aka sgmunson) 🙂 🙂 🙂
Rent Servers for Income (picks and shovels strategy)
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