Select Hex/Char conversion - sql-server

Question

I have some data in a SQL database stored in the format below, which I would like to convert to a readable string:
540045005300540049004E00470031003200330034
I would like to run some kind of SELECT statement to return the text which should be TESTING1234
It appears to be in Hex format separated by 00 between each character, so if I run these statements:
SELECT CHAR(0x54)
SELECT CHAR(0x45)
This returns:
T
E
Is there any way I can convert the whole string in one statement?
Thanks!

Answer 1

The 00 point to 2-byte-enocding which is represented as NVARCHAR. Try this
SELECT CAST(0x540045005300540049004E00470031003200330034 AS NVARCHAR(MAX))
Or directly from the HEX-string as string:
SELECT CAST(CONVERT(VARBINARY(MAX),'540045005300540049004E00470031003200330034',2) AS NVARCHAR(MAX));
The result is TESTING1234
Some more background on string encoding
SQL-Server knows exactly two types of strings:
1-byte-encoded VARCHAR / CHAR
2-byte-encoded nVARCHAR / nCHAR
The 1-byte string is extended ASCII, the related collation provides a code page to map non-plain-latin characters (it is not utf-8 as people sometimes tell).
The 2-byte string is UCS-2 (almost the same as utf-16).
I've corrected the word unicode above, as it is not correct actually.
There are many encodings SQL-Server will not be able to interpret natively.
The string above looks like it is good for NVARCHAR, but this is not guaranteed in any case.
Some more background on binary encoding
SQL-Server knows BINARY and VARBINARY as a real BLOB-Type. In the result of a SELECT they are presented as HEX-string and in a script you can use a HEX-string as native input. But it is important to know, that this HEX-string is not the actual value!, just the human readable representation on a computer screen.
And there is a real string, which looks like a HEX-string (but isn't).
0x123 != '0x123'
If you have a string, which is a HEX-string, but is coming to you as "normal" string (e.g. in a text based container like a CSV file or an XML) you have to convert this.
And, not really related to this question, just to mention it: There are more string based binary representers like base64.
Some examples
--start with a normal string
DECLARE #str VARCHAR(100)='This is a test to explain conversions from string to hex to binary and back';
--see the HEX string (real binary!)
SELECT CAST(#str AS VARBINARY(MAX)) ThisIsTheHexStringOfTheString;
--I copy the binary behind the "=" _wihtout_ quotes
DECLARE #ThisIsTheBinary VARBINARY(MAX)=0x546869732069732061207465737420746F206578706C61696E20636F6E76657273696F6E732066726F6D20737472696E6720746F2068657820746F2062696E61727920616E64206261636B;
--This can be re-casted directly
SELECT CAST(#ThisIsTheBinary AS VARCHAR(MAX)) ThisIsReconvertedBinary;
--there is an undocumented function providing a HEX-string from a binary
DECLARE #aHEXstring VARCHAR(MAX)=sys.fn_varbintohexstr(CAST(#str AS VARBINARY(MAX)));
--This string looks exactly the same as above, but it is a string
SELECT #aHEXstring AS ThisIsStringWhichLooksLikeHEX;
--You can use dynamic SQL
EXEC('SELECT CAST(' + #aHEXstring + ' AS VARCHAR(MAX)) AS CastedViaDynamicSQL');
--or CONVERT's abilities (read the documentation!)
SELECT CAST(CONVERT(VARBINARY(MAX),#aHEXstring,1) AS VARCHAR(MAX)) AS ConvertedViaCONVERT