Retrieve varbinary value as BASE64 in MSSQL

Question

I'm looking for a way for retrieving Entity Data Model (EDM) from __MigrationHistory table using only T-SQL (so anyone, using Microsoft SQL Server Management Studio only, could do the same).

I want to have a valid BASE64 string value.

I don't want to fully decompress it to EDMX.

I don't want to get it from *.resx migration file.

When I select whole __MigrationHistory in SSMS, Model column value is like following

0x1F8B0800000000000400CD57DB6EDB38107D5F60FF81E0D31648C5247DD906528BD4898BA075525469DF6969EC10CB8BCA4B607F5B1FFA49FB0B3BBACB521CB7E9A228020422357366E6F0CC50FEF7EBB7F8F54649720FD609A3137A121D53023A33B9D0EB8406BF7AFE377DFDEACF3FE2CB5C6DC8E7D6EE4569879EDA25F4CEFBE28C3197DD81E22E5222B3C699958F32A318CF0D3B3D3E7EC94E4E182004452C42E28F417BA1A05AE072667406850F5C2E4C0ED235FBF826AD50C93557E00A9E414253AE0A0917DCF325771035CB254278D8784ACEA5E098550A724509D7DA78EE31E7B34F0E526F8D5EA7056E7079BB2D00ED565C3A686A39EBCDBFB7ACE3D3B22CD63BB6505970DEA81F043C79D1F0C4C6EE4F629B763C229397C8B8DF9655576C26746E0C25E3386733694B9B433C47159C001721CC11D9353EEA84827A2AFF8EC82C481F2C241A82B75C1E910F612945F60EB6B7E61FD0890E520ED3C584F1DDCE066E7DB0A600EBB71F61D514719553C276FDD8D8B1731BF8D435BE0D029FAF31365F4AE8C4C01E752FFFB700A8286C144A167CF31EF4DADF25141F29998B0DE4ED4E83FA490BEC2B74F2368C82C4AC3F9DE999959473A1C136094C243F3944D47A738EAE09B75B518D9B82EFA5E028E973A8DB27AA14F2509E5D467DA3B2BA53DB8E667B5A3A5EF0A240CA062DDEEC90B4EEEFD9F3F4C7C5AE6A0C96B90734DF65DB45F2C6F2358CDE6268CC742EACF3AD902999E56A6236E67F0FB76DB401C5633DF78CB7C6E5F3CE29EFEBBFF26C46703D97732C4F81F655A5D06554F7FCC4AB1AB35C72FB409FCC8C0C4AEFEBB5C7BCEB3619FAD73B5384988DD21ED3C4263C8D3A7ECCF963921D9B74D13BE98E241A3772397C354DF4539B5082D4DC8BBCD2CED67950516910A55FE44C0AACB73758702D56E07C3D1429DE08A7A31BEDF7B95D9873B93C7CC5FCF2A11EB4F81200D9C46C5602EC4F0D787DCF6D76C7ED5F8A6F9E0D917E76884F67CDC111BD6F42D72A4B68BEC4C56D9D5E3DD19F38BBA7828FD9F08B2DBE0027D63D44F9FDA6212B95D483B636577A655A82B19C6146ADC988FF05789E232BE7160F90671E5F67E05C75D17EE632A0C9A55A427EA56F822F823F770ED4526E87F5C6ECF1F8D505B59B737C53942BF77F9480690A2C016EF49B2064DEE53D9FEA6F1F442990B780FB5587E28706C2ADB71DD2B5D1DF09D4D0770105E8B2296E016F120473373AE5F7F094DCF0FBE23DAC79B66DE7D67E90C307B14B7B7C21F8DA72E51A8CDEBFFC15C2CA9F21AFFE038574340FB80C0000

This is my sample database, so I don't mind sharing it.

The column is of type varbinary(max), I googled how can convert it to UTF8*-ish* text.

varbinary to string on SQL Server

SQL Server: Convert a string into a hex string and back #sql #sqlserver

For

SELECT CONVERT(VARCHAR(max), 0x1F8B0800000000000400CD57DB6EDB3810..... , 0)

or even more straightforward

SELECT CONVERT(VARCHAR(max), (SELECT TOP (1) [t0].[Model]FROM [__MigrationHistory] AS [t0]), 0);

I get the following result

literally this: ‹

I checked my Model if it's not broken or incomplete in both LinqPad5 and using this tool found here, but it looks ok.

Answer 1

Finally found this article:

https://social.technet.microsoft.com/wiki/contents/articles/36388.transact-sql-convert-varbinary-to-base64-string-and-vice-versa.aspx#Convert_VARBINARY_to_Base64_String

So, running the query gets what I wanted, valid Base64.

Using XML and the hint "for xml path"

select Model, baze64
from __MigrationHistory
cross apply (select Model as '*' for xml path('')) T (baze64)

Other presented queries in article will also work

Using XML XQuery

Using JSON

Answer 2

It's apparently gzip'd xml. eg

SELECT MigrationId
      ,ContextKey
      ,cast(decompress(model) as xml) model
  FROM __MigrationHistory

Answer 3

Based on your solution I'm sharing the code for 2 scalar function for conversion in both direction:

Base64Decode

CREATE FUNCTION [dbo].[fnBase64ToBinary]
(
    @Str AS NVARCHAR(MAX)
)
RETURNS VARBINARY(MAX)
AS
BEGIN
    RETURN (
        SELECT
                CONVERT(
                    VARBINARY(MAX), CAST('' AS XML).value('xs:base64Binary(sql:column("BASE64_COLUMN"))', 'VARBINARY(MAX)')
                )
        FROM    (SELECT @Str AS BASE64_COLUMN) A
    );
END;

Base64 encode

CREATE FUNCTION [dbo].[fnBinaryToBase64]
(
    @Var AS VARBINARY(MAX)
)
RETURNS NVARCHAR(MAX)
AS
BEGIN
    RETURN (
        SELECT  @Var AS '*' FOR XML PATH('')
    );
END;