MYSQL Checking even/odd within a substring - mysql

Question

I have a query where one condition to check if a room number is odd/even. The issue is that the room number is stored with the building info as well in a string.
Here is the format of the data in the database:
ABC-0101A (Odd)
ABC-0112B (Even)
ZYX-123A1 (Odd)
ZYX-456B1 (Even)
For a room number to be considered even/odd, it is dependent on the last number before the first letter after the dash.

Answer 1

This would be quite a lot easier and more performant if you could separately store the numeric portion in another column. As a long term solution, I would recommend doing that.
But you can use a regular expression here to match the last digit before the first number, with a set of even [02468] and a set of odd [13579] with a CASE statement.
SELECT
CASE
WHEN room REGEXP '-[0-9]*[02468][A-Z]' THEN 'even'
WHEN room REGEXP '-[0-9]*[13579][A-Z]' THEN 'odd'
ELSE 'something else entirely'
END
FROM rooms
The pattern -[0-9]* matches a literal hyphen followed by zero or more digits. Then the significant part is the [02468] or [13579] set to match an even or odd digit that must be present immediately preceding [A-Z] matching the next letter.
Here's a demonstration: http://sqlfiddle.com/#!9/464d1d/3
Exmaple matching an even room:
SELECT 'ABC-0112B' REGEXP '-[0-9]*[02468][A-Z]';
+------------------------------------------+
| 'ABC-0112B' REGEXP '-[0-9]*[02468][A-Z]' |
+------------------------------------------+
| 1 |
+------------------------------------------+
Example matching an odd room:
SELECT 'ABC-0101A' REGEXP '-[0-9]*[13579][A-Z]';
+------------------------------------------+
| 'ABC-0101A' REGEXP '-[0-9]*[13579][A-Z]' |
+------------------------------------------+
| 1 |
+------------------------------------------+
Example matching an odd room that doesn't end with a letter:
SELECT 'ABC-0101A11' REGEXP '-[0-9]*[13579][A-Z]';
+--------------------------------------------+
| 'ABC-0101A11' REGEXP '-[0-9]*[13579][A-Z]' |
+--------------------------------------------+
| 1 |
+--------------------------------------------+

Answer 2

First create a function IsNumeric which returns 1 if number is integer otherwise 0:
CREATE FUNCTION IsNumeric (input varchar(1024)) RETURNS int
RETURN input REGEXP '^(-|\\+){0,1}([0-9]+\\.[0-9]*|[0-9]*\\.[0-9]+|[0-9]+)$';
Then use following query to check room number:
select IF (IsNumeric(right(room,1))>0,
IF(right(room,1)%2=0,'Even','ODD'),
IF(left(right(room,2),1)%2=0,'Even','ODD')
) as room_number
from rooms;
Here in above query first check if last digit is integer, If so then check for even/Odd number. If digit is not integer pick the 2nd last digit and apply the same check.