I am using code like this in my SELECT statement:
CAST(HASHBYTES(N'SHA1', Bla) AS NVARCHAR(MAX)) AS hashed_bla
and end-up with "chinese"/UTF encoded characters in the ssms grid but also in upstream apps. Is there a way to change this? Does this have to do with the collation? Thanks!
What you have is working as expected. Take the following example:
SELECT HASHBYTES('SHA1','B8187F0D-5DBA-4D43-95FC-CD5A009DB98C');
This returns the varbinary value 0xA04B9CB18A2DC4BC08B83FCCE48A0AF1A1390756. You are then converting that value to an nvarchar, so get a result like N'䮠놜ⶊ별레찿諤㦡嘇' (on my collation). For an varbinary each 4 characters represents a single character. So, for the above A04B is the first character (which is N'䮠').
It appears what you are after is an varchar representing a varbinary value (you don't need an nvarchar here, as there will be no unicode characters). To do so, you need to use CONVERT and a style code. For the example I gave above that would be:
SELECT CONVERT(varchar(100),HASHBYTES('SHA1','B8187F0D-5DBA-4D43-95FC-CD5A009DB98C'),1);
Which returns the varchar value '0xA04B9CB18A2DC4BC08B83FCCE48A0AF1A1390756'. If you don't want the '0x' at the start, use style code 2, rather than 1.
Related
I have seen prefix N in some insert T-SQL queries. Many people have used N before inserting the value in a table.
I searched, but I was not able to understand what is the purpose of including the N before inserting any strings into the table.
INSERT INTO Personnel.Employees
VALUES(N'29730', N'Philippe', N'Horsford', 20.05, 1),
What purpose does this 'N' prefix serve, and when should it be used?
It's declaring the string as nvarchar data type, rather than varchar
You may have seen Transact-SQL code that passes strings around using
an N prefix. This denotes that the subsequent string is in Unicode
(the N actually stands for National language character set). Which
means that you are passing an NCHAR, NVARCHAR or NTEXT value, as
opposed to CHAR, VARCHAR or TEXT.
To quote from Microsoft:
Prefix Unicode character string constants with the letter N. Without
the N prefix, the string is converted to the default code page of the
database. This default code page may not recognize certain characters.
If you want to know the difference between these two data types, see this SO post:
What is the difference between varchar and nvarchar?
Let me tell you an annoying thing that happened with the N' prefix - I wasn't able to fix it for two days.
My database collation is SQL_Latin1_General_CP1_CI_AS.
It has a table with a column called MyCol1. It is an Nvarchar
This query fails to match Exact Value That Exists.
SELECT TOP 1 * FROM myTable1 WHERE MyCol1 = 'ESKİ'
// 0 result
using prefix N'' fixes it
SELECT TOP 1 * FROM myTable1 WHERE MyCol1 = N'ESKİ'
// 1 result - found!!!!
Why? Because latin1_general doesn't have big dotted İ that's why it fails I suppose.
1. Performance:
Assume your where clause is like this:
WHERE NAME='JON'
If the NAME column is of any type other than nvarchar or nchar, then you should not specify the N prefix. However, if the NAME column is of type nvarchar or nchar, then if you do not specify the N prefix, then 'JON' is treated as non-unicode. This means the data type of NAME column and string 'JON' are different and so SQL Server implicitly converts one operand’s type to the other. If the SQL Server converts the literal’s type
to the column’s type then there is no issue, but if it does the other way then performance will get hurt because the column's index (if available) wont be used.
2. Character set:
If the column is of type nvarchar or nchar, then always use the prefix N while specifying the character string in the WHERE criteria/UPDATE/INSERT clause. If you do not do this and one of the characters in your string is unicode (like international characters - example - ā) then it will fail or suffer data corruption.
Assuming the value is nvarchar type for that only we are using N''
I have seen prefix N in some insert T-SQL queries. Many people have used N before inserting the value in a table.
I searched, but I was not able to understand what is the purpose of including the N before inserting any strings into the table.
INSERT INTO Personnel.Employees
VALUES(N'29730', N'Philippe', N'Horsford', 20.05, 1),
What purpose does this 'N' prefix serve, and when should it be used?
It's declaring the string as nvarchar data type, rather than varchar
You may have seen Transact-SQL code that passes strings around using
an N prefix. This denotes that the subsequent string is in Unicode
(the N actually stands for National language character set). Which
means that you are passing an NCHAR, NVARCHAR or NTEXT value, as
opposed to CHAR, VARCHAR or TEXT.
To quote from Microsoft:
Prefix Unicode character string constants with the letter N. Without
the N prefix, the string is converted to the default code page of the
database. This default code page may not recognize certain characters.
If you want to know the difference between these two data types, see this SO post:
What is the difference between varchar and nvarchar?
Let me tell you an annoying thing that happened with the N' prefix - I wasn't able to fix it for two days.
My database collation is SQL_Latin1_General_CP1_CI_AS.
It has a table with a column called MyCol1. It is an Nvarchar
This query fails to match Exact Value That Exists.
SELECT TOP 1 * FROM myTable1 WHERE MyCol1 = 'ESKİ'
// 0 result
using prefix N'' fixes it
SELECT TOP 1 * FROM myTable1 WHERE MyCol1 = N'ESKİ'
// 1 result - found!!!!
Why? Because latin1_general doesn't have big dotted İ that's why it fails I suppose.
1. Performance:
Assume your where clause is like this:
WHERE NAME='JON'
If the NAME column is of any type other than nvarchar or nchar, then you should not specify the N prefix. However, if the NAME column is of type nvarchar or nchar, then if you do not specify the N prefix, then 'JON' is treated as non-unicode. This means the data type of NAME column and string 'JON' are different and so SQL Server implicitly converts one operand’s type to the other. If the SQL Server converts the literal’s type
to the column’s type then there is no issue, but if it does the other way then performance will get hurt because the column's index (if available) wont be used.
2. Character set:
If the column is of type nvarchar or nchar, then always use the prefix N while specifying the character string in the WHERE criteria/UPDATE/INSERT clause. If you do not do this and one of the characters in your string is unicode (like international characters - example - ā) then it will fail or suffer data corruption.
Assuming the value is nvarchar type for that only we are using N''
I need to subtract two nvarchar values and store the result in another column. I understand that first I need to convert nvarchar to numeric values, but I always get this error
Error converting data type nvarchar to real
Just to mention in varchar values are stored only numeric values but I can't seem to get this conversion right.
This looks like a SQL Server error. If so, use try_convert():
select try_convert(real, string_col)
This returns NULL instead of an error if there are conversion issues.
You can find the offending values using:
select string_col
from t
where try_convert(real, string_col) is null and
string_col is not null;
use a case statement. It should be something like (t-sql pseudo code inside a SELECT)
case when IsNumeric(column1) AND IsNumeric(column2)
then cast(column1 as decimal) - cast(column2 as decimal)
else NULL end as column3
This is a classical example of why you shouldn't mix types (nvarchar and decimal in this case), there are all sorts of shananigans - like ('abc' - 5) or (NULL - NULL) or ('five' - '3 '). If this works, it might be a good idea to look at the "NULL" results, as this might give you valuable insights as to what kind of garbage is being collected in your system.
You said that...
Just to mention in varchar values are stored only numeric values but I
can't seem to get this conversion right.
If that is absolutely true, then there's a very high probability that there are 1 or 2 trailing control characters (Tab, Carriage Return, Line Feed, whatever) in the items causing the errors.
Try converting the NVARCHAR values to the MONEY datatype first. It won't work for leading control characters but it will for trailing control characters. Obvioussly your original original value doesn't haven more than 4 decimal places, of course.
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 a little green when it comes to SQL Server string manipulation functions. If I have a string with six characters in it, say:
DECLARE #p_MyStringVariable VARCHAR (100)
SET #p_MyStringVariable = 'FANFFF'
And I want to insert, say, the letter 'M' in the first and seventh positions of the final string and assign that to another VARCHAR variable to read 'MFANFFMF', how can I best do that? And am I correct in reading that SQL Server strings are indexed starting from one, instead of zero? I'm thinking of the SUBSTRING() function, for instance.
(Note that some strings will be up to 100 characters in length, thus the VARCHAR(100) declaration above, even for a six-character string)
Thanks much for your help.
You could also take a look at the STUFF function.
SELECT STUFF(STUFF(#p_MyStringVariable,1,0,'M'),7,0,'M')
Yes, SQL Server indexes varchar etc columns starting at one.
To insert at specfic points, use STUFF (and see Joes's answer for examples)