Having trouble converting strings to numbers - sql

Question

I am having an issue with casting or converting my varchar2 value to a number. The problem is that my TO_EMPLOYEE column (in PROJ_NOTIFY_HIST) contains both email addresses and employee IDs.
SELECT NOTIFY.PROJ_ID
FROM PROJ_NOTIFY_HIST NOTIFY
WHERE NOTIFY.NOTIFIED_SENT = 0
AND CAST(NOTIFY.TO_EMPLOYEE AS NUMBER) NOT IN (SELECT EMPLOYEE_ID
FROM V_ACTIVE_EMPLOYEE_INFO);
Is there any way to get employee IDs only, and compare them to my sub-query?

Answer 1

You could test each to_employee value to see if it consists of only numeric characters, and only then try to convert it to a number and compare with your view. In recent versions of Oracle you can just use to_number() and use its default ... on error clause to prevent the ORA-01722. Or validate_conversion() to do the test.
But that will only tell you if the value is numeric, not if it is an employee ID which you can then check to see if it's active. You could have other numbers in there that aren't supposed to be IDs, like phone numbers for example.
if you have a table that contains all employee IDs, not just the active ones, then you could cast those the other way, from numbers to strings, to find matches; e.g. if you have an employee_info table that holds all active and inactive employees, something like:
select notify.proj_id
from proj_notify_hist notify
join employee_info e
on notify.to_employee = cast(e.employee_id as varchar2(10)) -- use suitable size
where notify.notified_sent = 0
and e.employee_id not in (select employee_id
from v_active_employee_info);
or
select notify.proj_id
from proj_notify_hist notify
join employee_info e
on notify.to_employee = cast(e.employee_id as varchar2(10)) -- use suitable size
where notify.notified_sent = 0
and not exists (select null
from v_active_employee_info active
where active.employee_id = e.employee_id);
If v_active_employee_info is a view over the employee_info table then you could skip that not in or exists look-up and instead directly test for whatever conditions the view is using to filter active employees.

Answer 2

I suspect you want something like this:
SELECT NOTIFY.PROJ_ID
FROM PROJ_NOTIFY_HIST NOTIFY
WHERE NOTIFY.NOTIFIED_SENT = 0 AND
NOT EXIST (SELECT 1
FROM V_ACTIVE_EMPLOYEE_INFO A
WHERE TO_CHAR(A.EMPLOYEE_ID) = NOTIFY.TO_EMPLOYEE
);
The main thing? Cast to a string not a number.
If you only want to limit this to values that look like a number, then:
SELECT NOTIFY.PROJ_ID
FROM PROJ_NOTIFY_HIST NOTIFY
WHERE NOTIFY.NOTIFIED_SENT = 0 AND
REGEXP_LIKE(EMPLOYEE_ID, '^[0-9]+$') AND
NOT EXIST (SELECT 1
FROM V_ACTIVE_EMPLOYEE_INFO A
WHERE TO_CHAR(A.EMPLOYEE_ID) = NOTIFY.TO_EMPLOYEE
);

Answer 3

Use case stetment to check should you convert it (field consists onlu numbers) or not.
CASE [ expression ]
WHEN condition_1 THEN result_1
ELSE result
END