How to convert varbinary(max) to base64 SQL Server 2014 - sql-server

Question

I have an Image saved as varbinary(max) in SQL Server 2014:
0xFFD8FFE115064578696600004D4D002A0000000800070...........
I want to convert it to Base64 To use it in Flutter.
I tried
SELECT CAST('' as varbinary(max)) FOR XML PATH(''), BINARY BASE64
and get :
MHhGRkQ4RkZFMTE1MDY0NTc4Njk2NjAwMDA0RDREMDAyQTAwMDAwMDA4MDAwN..........
But according to this site I should get:
/9j/4RUGRXhpZgAATU0AKgAAAAgABwESAAMAAAABAAEAAAEaAAUAAAABAAAAYgEbAA........
So how to convert varbinary(max) to base64?

Answer 1

Why are you attempting to CAST() the varbinary data? You just need to select it as an element or an attribute for the varbinary value to get base64 encoded...
/*
* Data setup...
*/
if object_id('tempdb..#demo') is not null
drop table #demo;
create table #demo (
fancyImage varbinary(max)
);
insert #demo (fancyImage) values (0xFFD8FFE115064578696600004D4D002A000000080007);
/*
* Select as an element containing base64 data
*/
select fancyImage as [base64DemoElement]
from #demo
for xml path(''), binary base64;
/*
* Select as an attribute containing base64 data
*/
select fancyImage as [#base64Attribute]
from #demo
for xml path('demoElement'), binary base64;
The first select outputs the base data in an element:
<base64DemoElement>/9j/4RUGRXhpZgAATU0AKgAAAAgABw==</base64DemoElement>
The second select outputs the base64 data in an attribute:
<demoElement base64Attribute="/9j/4RUGRXhpZgAATU0AKgAAAAgABw==" />
Following comments discussion with #DaleK, a third alternative to return the bare base64 characters without any XML tags:
select (
select top 1 cast(fancyImage as varbinary(max)) as [base64DemoElement]
from #demo
for xml path(''), type, binary base64
).value('.', 'varchar(max)') as [Base64 characters];
Which outputs:
Base64 characters
/9j/4RUGRXhpZgAATU0AKgAAAAgABw==

Answer 2

To select a bare Bas64 value in SQL Server, without any XML node, you just need an unnamed column in FOR XML
SELECT CAST(fancyImage AS varbinary(max))
FROM #demo
FOR XML PATH(''), BINARY BASE64;
Or as a correlated subquery
SELECT
myBase64 = (
SELECT CAST(fancyImage AS varbinary(max))
FOR XML PATH(''), BINARY BASE64
)
FROM #demo;
db<>fiddle

Answer 3

I think it was v2008 of SQL-Server, when base64 was made the default in XML for binaries (before it was a hex string). No need to specify this explicitly.
(The option BINARY BASE64 is needed with mode AUTO...)
Just to demonstrate the back and forth I declare some text (a chain of characters) and cast it to binary (the same chain of bytes, but not a string any more):
DECLARE #someText VARCHAR(100) = 'This is just some text...';
DECLARE #binary VARBINARY(MAX) = CAST(#someText AS VARBINARY(MAX));
--In this case it's okay to rely on implicit casting: easy approach
DECLARE #base64_easy VARCHAR(100) = (SELECT #binary FOR XML PATH(''));
--Just to demonstrate that the base64 we found (VGhpcyBpcyBqdXN0IHNvbWUgdGV4dC4uLg==) is correct we reconvert it simply by casting it to XML and using .value() to retrieve it as binary:
DECLARE #reConverted VARBINARY(MAX) = (SELECT CAST(#base64_easy AS XML).value('.','varbinary(max)'));
--Casting this chain of bytes into a varchar again will show its (unchanged) content:
SELECT CAST(#reConverted AS VARCHAR(100));
All of this can be used within ad-hoc queries.
Hint:
The more explicit statement SELECTs the value into XML and reads this into text via .value()
(The ,type is needed to allow for XML methods)
DECLARE #base64 VARCHAR(100) = (SELECT #binary FOR XML PATH(''), type).value('.','nvarchar(max)'); --VGhpcyBpcyBqdXN0IHNvbWUgdGV4dC4uLg==