I have a mobile chat conversation text area which is stored in ntext data type in SQL Server 2008. I am doing some process character by character. I need to do something I do not know to pass these kind of emoji characters. Should I eliminate them or collate to different collation or encode to different char-set. My table's collation type is Latin1_General_CI_AS. I need something like this:
IF(SUBSTRING(#chat_Conversation, #i, 1) = 'Emoji')
CONTINUE;
As a first guess I'd suggest to place an N in front of your literal
Compare the results:
SELECT '😊'
,N'😊';
The result
ExtASCII Unicode
?? 😊
Without the N the literal is read as extended ASCII, unknown characters are returned as question marks. With N you are dealing with UNICODE (to be exact: UCS-2)...
UPDATE
As pointed out in comments: Do not use NTEXT!
NTEXT, TEXT and IMAGE are deprecated for centuries! These types will not be supported in future versions!
Convert all your work (columns, variables...) to
NTEXT -> NVARCHAR(MAX) (covering UCS-2 characters)
TEXT -> VARCHAR(MAX) (covering extended ASCII, depending on COLLATION and code page)
IMAGE -> VARBINARY(MAX) (covering BLOBs)
Hint
If you are dealing with special characters like foreign alphabets or emojis you should always use the N with literals and with types...
Related
In the SAP SQL Anywhere (where datatypes and most of the structures are very similar to SQL Server) the default database collation is set to UTF-8 - settings in detail below:
I have a set of special characters which the database needs to store and work with (range: U+1400 - U+167F) and after the test insert both VARCHAR and NVARCHAR datatypes were able to accommodate for these special characters with no visible difference (except the allocated space) - see below:
Do I understand correctly when DB collation is set to UTF-8 (with UTF8BIN charset) the CHAR/VARCHAR datatype is by default able to store UTF-8 charset and NCHAR/NVARCHAR the UTF-16? Meaning, I do not have to convert all CHAR/VARCHAR objects into NCHAR/NVARCHAR if all I need is the UTF-8 range: U+1400 - U+167F ?
To answer my own question:
Yes, CHAR and VARCHAR in UTF-8 Collation will store all characters but the datatype lenght specification will differ. When defining varchar lenght e.g.: VARCHAR(100) we expect 100 character string limit. This will only work for the characters where 1char = 1byte (ASCII), for all UTF-8 characters (2-4bytes) the number will specify the byte-lenght e.g.: VARCHAR(100) will be able to contain only UTF-8 string which is 25 characters long for 4-byte UTF-8 text.
Please feel free to correct me or improve my answer.
I have some data which I believe is Unicode and seeing what happens when I store it into my database column which is of VARCHAR(MAX) datatype.
And here's the source, from the file which is UTF-8...
looking for that ‘X’ and • 3 large bedrooms with 2 ensuites and • Main bedroom with ensuite & surround with plantation shutters`
and using the Visual Studio debugger:
=> so 2x apostrophes and 2x bullets.
I thought SQL Server can only store Unicode if the column is of type NVARCHAR?
I'm assuming my source data is not Unicode and therefore, I totally suck at all this Unicode/UTF-8 stuff :(
I thought SQL Server can only store Unicode if the column is of type NVARCHAR?
That's correct. As far as I can guess from your example, it is not storing Unicode. Probably it is storing bytes encoded in Windows code page 1252, which would be the default encoding for a Western install of SQL Server.
Code page 1252 happens to include mappings for characters ‘, ’ and •, so those characters can be safely stored. But step outside that limited repertoire and you'll start losing characters.
This is purely theoretical question to wrap my head around
Let's say I have Unicode cyclone (🌀 1F300) symbol. If I try to store it in varchar column that has default Latin1_General_CI_AS collation, cyclone symbol cannot not fit into one byte that is used per symbol in varchar...
The ways I can see this done:
Like javascript does for symbols out of Basic plane(BMP) where it stores them as 2 symbols (surrogate pairs), and then additional processing is needed to put them back together...
Just truncate the symbol, store first byte and drop the second.... (data is toast - you should have read the manual....)
Data is destroyed and nothing of use is saved... (data is toast - you should have read the manual....)
Some other option that is outside of my mental capacity.....
I have done some research after inserting couple of different unicode symbols
INSERT INTO [Table] (Field1)
VALUES ('👽')
INSERT INTO [Table] (Field1)
VALUES ('🌀')
and then reading them as bytes SELECT
cast (field1 as varbinary(10)) in both cases I got 0x3F3F.
3F in ascii is ? (question mark) e.g two question marks (??) that I also see when doing normal select * does that mean that data is toast and not even 1st bite is being stored?
How is Unicode data that is out of collation stored in varchar column?
The data is toast and is exactly what you see, 2 x 0x3F bytes. This happens during the type conversion prior to the insert and is effectively the same as cast('👽' as varbinary(2)) which is also 0xF3F3 (as opposed to casting N'👽').
When Unicode data must be inserted into non-Unicode columns, the columns are internally converted from Unicode by using the WideCharToMultiByte API and the code page associated with the collation. If a character cannot be represented on the given code page, the character is replaced by a question mark (?) Ref.
Yes the data has gone.
Varchar requires less space, compared to NVarchar. But that reduction comes at a cost. There is no space for a Varchar to store Unicode characters (at 1 byte per character the internal lookup just isn't big enough).
From Microsoft's Developer Network:
...consider using the Unicode nchar or nvarchar data types to minimize character conversion issues.
As you've spotted, unsupported characters are repalced with question marks.
I have a table with columns that contain both thai and english text data. NVARCHAR(255).
In SSMS I can query the table and return all the rows easy enough. But if I then query specifically for one of the Thai results it returns no rows.
SELECT TOP 1000 [Province]
,[District]
,[SubDistrict]
,[Branch ]
FROM [THDocuworldRego].[dbo].[allDistricsBranches]
Returns
Province District SubDistrict Branch
อุตรดิตถ์ ลับแล ศรีพนมมาศ Northern
Bangkok Khlong Toei Khlong Tan SSS1
But this query:
SELECT [Province]
,[District]
,[SubDistrict]
,[Branch ]
FROM [THDocuworldRego].[dbo].[allDistricsBranches]
where [Province] LIKE 'อุตรดิตถ์'
Returns no rows.
What do I need o do to get the expected results.
The collation set is Latin1_General_CI_AS.
The data is displayed and inserted with no errors just can't search.
Two problems:
The string being passed into the LIKE clause is VARCHAR due to not being prefixed with a capital "N". For example:
SELECT 'อุตรดิตถ์' AS [VARCHAR], N'อุตรดิตถ์' AS [NVARCHAR]
-- ????????? อุตรดิตถ
What is happening here is that when SQL Server is parsing the query batch, it needs to determine the exact type and value of all literals / constants. So it figures out that 12 is an INT and 12.0 is a NUMERIC, etc. It knows that N'ดิ' is NVARCHAR, which is an all-inclusive character set, so it takes the value as is. BUT, as noted before, 'ดิ' is VARCHAR, which is an 8-bit encoding, which means that the character set is controlled by a Code Page. For string literals and variables / parameters, the Code Page used for VARCHAR data is the Database's default Collation. If there are characters in the string that are not available on the Code Page used by the Database's default Collation, they are either converted to a "best fit" mapping, if such a mapping exists, else they become the default replacement character: ?.
Technically speaking, since the Database's default Collation controls string literals (and variables), and since there is a Code Page for "Thai" (available in Windows Collations), then it would be possible to have a VARCHAR string containing Thai characters (meaning: 'ดิ', without the "N" prefix, would work). But that would require changing the Database's default Collation, and that is A LOT more work than simply prefixing the string literal with "N".
For an in-depth look at this behavior, please see my two-part series:
Which Collation is Used to Convert NVARCHAR to VARCHAR in a WHERE Condition? (Part A of 2: “Duck”)
Which Collation is Used to Convert NVARCHAR to VARCHAR in a WHERE Condition? (Part B of 2: “Rabbit”)
You need to add the wildcard characters to both ends:
N'%อุตรดิตถ์%'
The end result will look like:
WHERE [Province] LIKE N'%อุตรดิตถ์%'
EDIT:
I just edited the question to format the "results" to be more readable. It now appears that the following might also work (since no wildcards are being used in the LIKE predicate in the question):
WHERE [Province] = N'อุตรดิตถ์'
EDIT 2:
A string (i.e. something inside of single-quotes) is VARCHAR if there is no "N" prefixed to the string literal. It doesn't matter what the destination datatype is (e.g. an NVARCHAR(255) column). The issue here is the datatype of the source data, and that source is a string literal. And unlike a string in .NET, SQL Server handles 'string' as an 8-bit encoding (VARCHAR; ASCII values 0 - 127 same across all Code Pages, Extended ASCII values 128 - 255 determined by the Code Page, and potentially 2-byte sequences for Double-Byte Character Sets) and N'string' as UTF-16 Little Endian (NVARCHAR; Unicode character set, 2-byte sequences for BMP characters 0 - 65535, two 2-byte sequences for Code Points above 65535). Using 'string' is the same as passing in a VARCHAR variable. For example:
DECLARE #ASCII VARCHAR(20);
SET #ASCII = N'อุตรดิตถ์';
SELECT #ASCII AS [ImplicitlyConverted]
-- ?????????
Could be a number of things!
Fist of print out the value of the column and your query string in hex.
SELECT convert(varbinary(20)Province) as stored convert(varbinary(20),'อุตรดิตถ์') as query from allDistricsBranches;
This should give you some insight to the problem. I think the most likely cause is the ั, ิ, characters being typed in the wrong sequence. They are displayed as part of the main letter but are stored internally as separate characters.
I'm dealing with unicode stuff in my DB. I have a data field defined as varchar(max),
and I'm preventing user to save unknown characters in this field, like "≤" for example (all unicode above U+00FF).
While doing so, I found that some characters if sent to be saved in this field would be displayed as "?", so I thought that all unicode characters above "U+00FF" will all be displayed like this, but then I found that "U+201B" which is "‛" is displayed "?" but the next character "U+201C" which is "“" is displayed as "“".
Can someone please explain to me why is that?
Update: Sorry if I was not clear, but I do not want to convert to nvarchar, I want to keep my field as varchar.
What I need to understand is why a character like "‛" is displayed as "?" in a "varchar" field while the next unicode character "“" is displayed properly?
If you want to store Unicode characters, you should use an nvarchar type, not varchar
You need to change your data type to nvarchar which will hold any unicode character where varchar is restricted to 8bit codepage.
For more information, read the accepted answer in this link below.
Difference between varchar and nvarchar