Fetching result from Oracle db - mysql

Question

I have a DB table
frequency table as follows
(companyid, task, and frequency) is unique key
| companyid| task |frequency | date |
| -------- | ----- | ------- | ----- |
| 123 | abc | Day | 03-03-2020 |
| 123 | def | Week | 09-03-2020 |
| 456 | abc | Week | 10-03-2020 |
| 456 | klm | Week | 12-03-2020 |
History table as follows PRIMARY KEY ("companyid", "RECORDNO")
| companyid| RECORDNO | STAGE | STATE |
| -------- | ----- | ------- | ----- |
| 123 | 12 | 1 | P |
| 456 | 13 | 2 | A |
| 123 | 13 | 1 | S |
Entry table , unique ("companyid", "ID")
| companyid| ID | STATE | task |
| -------- | ----- | ----- | ----- |
| 123 | 12 | Purchased | abc |
| 123 | 13 | Accesible | def |
| 456 | 13 | Store | abc |
| 456 | 14 | Store | klm |
I am running a job that frequently runs every 6 hours.
I have to fetch unique companyids where the state in history table is 'S' and has the task in frequency = task in entry table and recordno is history table = id in entry table and current system date is greater than the date in the frequency table.
The basic need is to process the job(entries from entry table) which has less date than the current system date. (Note the system date is always in UTC and date in frequency table can be configured by the user).
companyid is common in all tables.
I have tried the below query to fetch the result without having the date filters.
Need help in getting the time filter properly.
select distinct cny#
from frequency
where exists
(select 1
from history, entry
where history.companyid = entry.companyid
and history.state='S'
and history.record# = entry.id);

Answer 1

You can use oracle sysdate function to get the current date and time of the database server, and use it in the query.
select distinct companyid
from frequency
where exists
(select 1
from history, entry
where history.companyid = entry.companyid
and history.state='S'
and history.recordno = entry.id)
and sysdate > to_date(date,'DD-MM-YYYY');

Answer 2

Isn't this a simple join of the three tables?
select distinct e.company_id
from entry e
join history h on h.companyid = e.companyid and h,recordno = e.id
join frequency f on f.companyid = e.companyid and f.task = e.task
where f.date < trunc(sysdate)
and h.state = 'S';
or with the criteria in the ON clauses:
select distinct e.company_id
from entry e
join history h on h.companyid = e.companyid and h,recordno = e.id and h.state = 'S'
join frequency f on f.companyid = e.companyid and f.task = e.task and f.date < trunc(sysdate)
;
Usually, though, you'd have a company table, so you wouldn't need DISTINCT:
select * from company where companyid in (select e.companyid from ...);