this article may help you

https://www.codeproject.com/Articles/20815/Building-Dynamic-SQL-In-a-Stored-Procedure

some similar posts from you 
https://www.sqlservercentral.com/Forums/1818860/need-to-extract-text-from-given-string

https://www.sqlservercentral.com/Forums/1882790/Extract-String

just a thought.........probably way off base !

SELECT TOP 30 PG_ID = IDENTITY( INT, 1, 1)
INTO #PG
FROM sys.all_columns;

SELECT * FROM #PG;

DELETE...

I have to ask why you are performing this query

SELECT *
FROM calendar
UNION
SELECT *
FROM calendar

are you by chance trying to obfuscate an...

based on what I believe you have said so far in this post...is the following a representative example? 

SELECT TOP 420000
TransDate = Dateadd(dd, Abs(Checksum(Newid()))%Datediff(dd, '2015', '2017'), '2015')

some discussion here

https://www.sqlservercentral.com/Forums/1867110/Performing-a-Right-and-Comprehensive-Age-Calculation

does this help at all?

INSERT INTO hashed(id, sha256)
SELECT id, convert(varchar(280), HASHBYTES('SHA2_256',id),1)
FROM [nonhashed] ;

see "Binary style" on this page:

using CASE

DECLARE @yourtable TABLE
(colA INT,
colB INT,
colC INT
);
INSERT INTO @yourtable
VALUES
(100, 300, 200),
(400, 100, 200),
(500, 500, 600)
;

not sure if I am on the right track ..

DECLARE @yourtable TABLE
(source_database_id VARCHAR(20),
target_database_id VARCHAR(50)
);
INSERT INTO @yourtable
VALUES
('WDICENTRAL', 'WDIFINAL'),('WDIFINAL', 'WDICENTRAL'),
('GDFADVWKG', 'WDIFINAL'),('SOCQNT',...

thanks for updated script...it works🙂

based on your sample data...what results are you expecting, please?