declare @tab table (col1 char(2))

insert into @tab values

('A1'),

('A2'),

('A3'),

('B1'),

('B2'),

('B3')

SELECT

A.Col1,

B.Col1

FROM

(

SELECT

ROW_NUMBER() OVER(PARTITION BY LEFT(Col1,1) ORDER BY Col1) AS RowNum,

Col1

FROM

@tab

WHERE

LEFT(Col1,1) = 'A'

) AS A

FULL OUTER JOIN

(

SELECT

ROW_NUMBER() OVER(PARTITION BY LEFT(Col1,1) ORDER BY Col1) AS RowNum,

Col1

FROM

@tab

WHERE

LEFT(Col1,1) = 'B'

) AS B

ON

A.RowNum = B.RowNum