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@sevaa
Last active Feb 9, 2022
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Converting an NVARCHAR string to a UTF-8 VARBINARY data block in pure Transact-SQL
create function [dbo].[ToUTF8](@s nvarchar(max))
returns varbinary(max)
as
begin
declare @i int = 1, @n int = datalength(@s)/2, @r varbinary(max) = 0x, @c int, @c2 int, @d varbinary(4)
while @i <= @n
begin
set @c = unicode(substring(@s, @i, 1))
if (@c & 0xFC00) = 0xD800
begin
set @i += 1
if @i > @n
return cast(cast('Malformed UTF-16 - two nchar sequence cut short' as int) as varbinary)
set @c2 = unicode(substring(@s, @i, 1))
if (@c2 & 0xFC00) <> 0xDC00
return cast(cast('Malformed UTF-16 - continuation missing in a two nchar sequence' as int) as varbinary)
set @c = (((@c & 0x3FF) * 0x400) | (@c2 & 0x3FF)) + 0x10000
end
if @c < 0x80
set @d = cast(@c as binary(1))
if @c >= 0x80 and @c < 0x800
set @d = cast(((@c * 4) & 0xFF00) | (@c & 0x3F) | 0xC080 as binary(2))
if @c >= 0x800 and @c < 0x10000
set @d = cast(((@c * 0x10) & 0xFF0000) | ((@c * 4) & 0x3F00) | (@c & 0x3F) | 0xe08080 as binary(3))
if @c >= 0x10000
set @d = cast(((@c * 0x40) & 0xFF000000) | ((@c * 0x10) & 0x3F0000) | ((@c * 4) & 0x3F00) | (@c & 0x3F) | 0xf0808080 as binary(4))
set @r += @d
set @i += 1
end
return @r
end
@sevaa
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sevaa commented Nov 7, 2016

Unlike the GitHub comment system, it works correctly with characters from Unicode's astral planes.

@isken99
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isken99 commented Oct 24, 2017

Hi Sevaa,
I worked in AP team needs to deal with Asia Characters.
I have tested your SQL function with few Korea and Chinese characters find out the encoding does not meet the internet URL encoding standard.

The left UTF8 is from standard URL encoding, the right one is from the function
〇 E38087 E3C087
ㄱ E384B1 E3C4B1
validated with http://memory.loc.gov/diglib/codetables/9.3.html

There seems to be a pattern of the wrong encoding on the second byte 80 -> C0 and 84 -> C4.

I am not familiar bitwise and hex calculation at all. I really hope to fix it. Will you be quickly discover why?

@isken99
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isken99 commented Oct 25, 2017

@sevaa
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sevaa commented Feb 4, 2018

Sorry didn't get to this earlier, only found this comment today. Fixed now, a mask was off in the 3- and 4-byte encoding.

@kmcconnell
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kmcconnell commented Jun 12, 2019

Truly a hidden gem. Many thanks for this!

@sevaa
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sevaa commented Jul 16, 2019

Here's a gist for the converse operation - from a UTF-8 VARBINARY to a NVARCHAR string: https://gist.github.com/sevaa/5a50ba98762762ae960b87fb148a7df2

@APoint2020
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APoint2020 commented Dec 29, 2020

Works perfectly 👍

@pvgoran
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pvgoran commented Oct 11, 2021

Isn't the handling of surrogate pairs incorrect here? According to https://en.wikipedia.org/wiki/UTF-16#Code_points_from_U+010000_to_U+10FFFF , 0x10000 should be added to the combination produced from two surrogate code units, rather than OR'ed with this combination.

Also, this code doesn't check that the second code unit is actually surrogate (or whether it exists at all), so it can produce unexpected/broken results if unpaired surrogate code units are encountered.

@sevaa
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sevaa commented Oct 11, 2021

I've added some checks for malformed UTF-16 surrogate pairs. The function will now throw a reasonably descriptive error instead of producing garbage outputs.

@sevaa
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sevaa commented Nov 7, 2021

Since MSSQL 2019, there is native support for UTF-8. The following will do the same job, most likely much faster:

declare @s nvarchar(100) = N'Москва 東京 🙃', @t varchar(200) 
set @t = CAST(@s AS varchar) collate Latin1_General_100_CI_AI_SC_UTF8
print @t

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