SQL: Create Customized Column Variable In SELECT - sql

Question

Trying to look for better way to store customized column (that called many times in queries) in SQL variable.
I’m using Oracle and I execute this query:
SELECT project,
( CASE
WHEN TO_CHAR((100 - round(value, 5) * 100)) NOT LIKE ‘.%’
THEN (100 - round(value, 5) * 100) || ‘%’
ELSE ‘0’ || (100 - round(value, 5) * 100) || ‘%’
END ) AS percentage
FROM table;
The customized column: 100 - round(value, 5) is called 3 times. In addition, That customized column called in many other SELECT queries in my project. Is there any option to save that customized column as a variable and call it in shorter way?
For example, I would like to do something like that:
SELECT project,
( CASE
WHEN TO_CHAR(CUSTOMIZED_VALUE) NOT LIKE ‘.%’
THEN CUSTOMIZED_VALUE || ‘%’
ELSE ‘0’ || CUSTOMIZED_VALUE || ‘%’
END ) AS percentage
FROM table;
Table Columns:
| Column | Type |
|:—————————|————————————:|
| project |VARCHAR2(100)|
| value | FLOAT(*) |
When value is always between 0 to 1.
Thank you for your help!

Answer 1

Add a virtual column:
ALTER TABLE table_name
ADD customized_value NUMBER GENERATED ALWAYS AS (100 - round(value, 5) * 100);
Which, if you have the table:
CREATE TABLE table_name (value) AS
SELECT 0.00 FROM DUAL UNION ALL
SELECT 0.42 FROM DUAL UNION ALL
SELECT 1.00 FROM DUAL;
Then, after you have added the column, when you query the table:
SELECT * FROM table_name;
The output is:
VALUE
CUSTOMIZED_VALUE
0
100
.42
58
1
0
And you can use CUSTOMIZED_VALUE in other, more complicated, expressions.
fiddle

Answer 2

You can define it in a sub-query (or a sub-query factoring clause) and then use it in an outer query:
SELECT project,
TO_CHAR(CUSTOMIZED_VALUE, 'FM990') || '%' AS percentage
FROM (
SELECT t.*,
100 - round(value, 5) * 100 AS customized_value
FROM table_name t
);
or:
WITH subquery_factoring_clause (project, value, customized_value) AS (
SELECT t.*,
100 - round(value, 5) * 100 AS customized_value
FROM table_name t
)
SELECT project,
TO_CHAR(CUSTOMIZED_VALUE, 'FM990') || '%' AS percentage
FROM subquery_factoring_clause;
Which, for the sample data:
CREATE TABLE table_name (project, value) AS
SELECT 'a', 0.00 FROM DUAL UNION ALL
SELECT 'b', 0.42 FROM DUAL UNION ALL
SELECT 'c', 1.00 FROM DUAL;
Outputs:
PROJECT
PERCENTAGE
a
100%
b
58%
c
0%
fiddle