Oracle Select Query based on a column value

I have two tables and wanted to conditionally query one of the tables.
For example below are the two tables with few matching columns in two tables
Table A(SNO, Number,Name…)
Table B ( SNO, Number,FullName..)
Number column value is passed to the query dynamically.
Table A and B have matching Columns(SNO,Number)
I would like to run a query on table based on the value of Number column which is common in both tables.

Something like this
if number =12
Select Query on Table A
else
select Query on Table B

SELECT *
FROM TABLE_A
WHERE number = 12
AND  {other conditions}
UNION
SELECT *
FROM TABLE_B
WHERE number != 12
AND  {other conditions}