# In the same view, how to use a calculated column to calculate another column

## Problem

I’m hoping you can assist me with this query. I’m working with Oracle SQL (SQL Developer for this view)…

If I have the following columns in a table:

In my opinion, I have

``````Select
ColumnA,
ColumnB,
ColumnA + ColumnB As calccolumn1
``````

I’d like to use calccolumn1 at this point, but I can’t just say…

``````Select
ColumnA,
ColumnB,
ColumnA + ColumnB As calccolumn1
calccolumn1 / ColumnC as calccolumn2
``````

I’m guessing I’ll need a subquery…but this is where I’ll need your aid… How should I phrase the query so that calccolumn1 can be used in another calculation within the same query? It may be an If then or a Case when, but at the end of the day, it’s a derived integer.

## Solution #1

A nested query could be used:

``````Select
ColumnA,
ColumnB,
calccolumn1,
calccolumn1 / ColumnC as calccolumn2
From (
Select
ColumnA,
ColumnB,
ColumnC,
ColumnA + ColumnB As calccolumn1
from t42
);
``````

With a row of 3, 4, and 5 values, you get:

``````   COLUMNA    COLUMNB CALCCOLUMN1 CALCCOLUMN2
---------- ---------- ----------- -----------
3          4           7         1.4
``````

Unless it’s truly doing something expensive (through a function call, for example), you may just repeat the initial calculation:

``````Select
ColumnA,
ColumnB,
ColumnA + ColumnB As calccolumn1,
(ColumnA + ColumnB) / ColumnC As calccolumn2
from t42;

COLUMNA    COLUMNB CALCCOLUMN1 CALCCOLUMN2
---------- ---------- ----------- -----------
3          4           7         1.4
``````

## Solution #2

In Sql Server

This can be accomplished with the help of cross apply.

``````Select
ColumnA,
ColumnB,
c.calccolumn1 As calccolumn1,
c.calccolumn1 / ColumnC As calccolumn2
from t42
cross apply (select (ColumnA + ColumnB) as calccolumn1) as c
``````

## Solution #3

If you want to refer to calculated column on the “same query level” then you could use CROSS APPLY(Oracle 12c):

``````--Sample data:
CREATE TABLE tab(ColumnA NUMBER(10,2),ColumnB NUMBER(10,2),ColumnC NUMBER(10,2));

INSERT INTO tab(ColumnA, ColumnB, ColumnC) VALUES (2, 10, 2);
INSERT INTO tab(ColumnA, ColumnB, ColumnC) VALUES (3, 15, 6);
INSERT INTO tab(ColumnA, ColumnB, ColumnC) VALUES (7, 14, 3);
COMMIT;
``````

Query:

``````SELECT
ColumnA,
ColumnB,
sub.calccolumn1,
sub.calccolumn1 / ColumnC AS calccolumn2
FROM tab t
CROSS APPLY (SELECT t.ColumnA + t.ColumnB AS calccolumn1 FROM dual) sub;
``````

DBFiddle Demo

Please notice that the CROSS APPLY/OUTER APPLY statement is also accessible in other clauses:

``````SELECT
ColumnA,
ColumnB,
sub.calccolumn1,
sub.calccolumn1 / ColumnC AS calccolumn2
FROM tab t
CROSS APPLY (SELECT t.ColumnA + t.ColumnB AS calccolumn1 FROM dual) sub
WHERE sub.calccolumn1 = 12;
-- GROUP BY ...
-- ORDER BY ...;
``````

This method eliminates the need to wrap the entire query in an outerquery or copy/paste the same expression many times (with complex one it could be hard to maintain).

Related article: The SQL Languageās Most Missing Feature

## Solution #4

The expression for your calculated column must be included:

``````SELECT
ColumnA,
ColumnB,
ColumnA + ColumnB AS calccolumn1
(ColumnA + ColumnB) / ColumnC AS calccolumn2
``````

## Solution #5

SQL Server is a database management system. This can be done with the use of CTE.

WITH common_table_expression (Transact-SQL)

``````CREATE TABLE tab(ColumnA DECIMAL(10,2), ColumnB DECIMAL(10,2), ColumnC DECIMAL(10,2))

INSERT INTO tab(ColumnA, ColumnB, ColumnC) VALUES (2, 10, 2),(3, 15, 6),(7, 14, 3)

WITH tab_CTE (ColumnA, ColumnB, ColumnC,calccolumn1)
AS
(
Select
ColumnA,
ColumnB,
ColumnC,
ColumnA + ColumnB As calccolumn1
from tab
)

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

DBFiddle Demo