SQL Server 2019

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DECLARE @query NVARCHAR(MAX) = '
SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = ''A''
AND CATEGORY2 = ''B''
'

PRINT @query

SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = 'A'
AND CATEGORY2 = 'B'



DECLARE @A nvarchar(10) = 'A'
DECLARE @B nvarchar(10) = 'B'

DECLARE @query NVARCHAR(MAX) = '
SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = ''' + @A + '''
AND CATEGORY2 = ''' + @B + '''
'

PRINT @query

SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = 'A'
AND CATEGORY2 = 'B'



DECLARE @A nvarchar(10) = 'Bob''s'
DECLARE @B nvarchar(10) = 'Peter''s'

DECLARE @query NVARCHAR(MAX) = '
SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = ''' + @A + '''
AND CATEGORY2 = ''' + @B + '''
'

PRINT @query  
-- Note @query is invalid as apostrophes in Bob's and Peter's need to be double

SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = 'Bob's'
AND CATEGORY2 = 'Peter's'



DECLARE @A nvarchar(10) = 'Bob''s'
DECLARE @B nvarchar(10) = 'Peter''s'

DECLARE @query NVARCHAR(MAX) = '
SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = ''' + REPLACE(@A,'''','''''') + '''
AND CATEGORY2 = ''' + REPLACE(@B,'''','''''') + '''
'

PRINT @query  -- query is now valid

SELECT CATEGORY1,CATEGORY2
FROM TABLE
WHERE CATEGORY1 = 'Bob''s'
AND CATEGORY2 = 'Peter''s'