SQL Server 2019

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CREATE TABLE tab(ColumnA DECIMAL(10,2), ColumnB DECIMAL(10,2), ColumnC DECIMAL(10,2))
INSERT INTO tab(ColumnA, ColumnB, ColumnC) VALUES (3, 4, 5),(3, 15, 6),(7, 14, 3)
3 rows affected

SELECT *
FROM tab


ColumnA
ColumnB
ColumnC


3.00
4.00
5.00

3.00
15.00
6.00

7.00
14.00
3.00


WITH tab_CTE (ColumnA, ColumnB, ColumnC,calccolumn1)  
AS  
-- Define the CTE query.  
(  
Select
    ColumnA,
    ColumnB,
    ColumnC,
    ColumnA + ColumnB As calccolumn1
  from tab
)  

SELECT
  ColumnA,
  ColumnB,
  calccolumn1,
  calccolumn1 / ColumnC AS calccolumn2
FROM tab_CTE



ColumnA
ColumnB
calccolumn1
calccolumn2


3.00
4.00
7.00
1.4000000000000

3.00
15.00
18.00
3.0000000000000

7.00
14.00
21.00
7.0000000000000

ColumnA	ColumnB	calccolumn1	calccolumn2
3.00	4.00	7.00	1.4000000000000
3.00	15.00	18.00	3.0000000000000
7.00	14.00	21.00	7.0000000000000