Oracle-Making condition optional in Select statement - sql

Question

How to make a condition optional?
That is, if a condition of the where clause is FALSE, how to ignore the condition in a simplest way?
The expected result of my code is,
RR
--
100
200
My Code is,
WITH DATASET AS (
SELECT 1 A, 10 B, 100 RR FROM DUAL
UNION
SELECT NULL A, 10 B, 200 RR FROM DUAL
)
SELECT RR
FROM DATASET
WHERE
A=2 -- How to make this condition optional(that is, as 2 is not found then,ignoring this condition)
AND
B=10
;

Answer 1

I understood that if not exists 2 in all data you do not want to filter but if there is a 2 in A column then you want to it.
so try this:
SOLUTION 1:
SELECT * FROM
(
WITH DATASET AS (
SELECT 1 A, 10 B, 100 RR FROM DUAL
UNION
SELECT NULL A, 10 B, 200 RR FROM DUAL
)
SELECT
RR
FROM
DATASET
WHERE B=10
AND EXISTS
(
SELECT 1 FROM DATASET WHERE A=2
)
)
UNION
SELECT * FROM
(
WITH DATASET AS (
SELECT 1 A, 10 B, 100 RR FROM DUAL
UNION
SELECT NULL A, 10 B, 200 RR FROM DUAL
)
SELECT
RR
FROM
DATASET
WHERE B=10
AND NOT EXISTS
(
SELECT 1 FROM DATASET WHERE A=2
)
)
SOLUTION2 :
WITH DATASET AS (
SELECT 1 A, 10 B, 100 RR FROM DUAL
UNION
SELECT NULL A, 10 B, 200 RR FROM DUAL
)
,SUB AS (
SELECT DISTINCT 1 A_EXISTS,RR
FROM DATASET
WHERE A=2
),
SUB2 AS (
SELECT DISTINCT
CASE
WHEN SUB.A_EXISTS IS NOT NULL AND DATASET.A=2
THEN SUB.RR
WHEN SUB.A_EXISTS IS NOT NULL AND DATASET.A<>2
THEN NULL
ELSE DATASET.RR
END RR
FROM
DATASET
FULL OUTER JOIN SUB ON A_EXISTS=1
WHERE DATASET.B=10
)
SELECT
*
FROM SUB2
WHERE RR IS NOT NULL