> Here’s one I used that should work in all SQL languages. I was trying to avoid using specific language stuff like EXISTS and DUPLICATE.
>
> It’s very simple. Just insert the value(s) where 0 equals the count of the value(s) already existing.
>
> INSERT INTO audit_type
> SELECT DISTINCT ‘sample’ FROM audit_type WHERE
> 0 = (SELECT COUNT(audit_type_desc) FROM audit_type WHERE audit_type_desc = ‘sample’)

This doesn’t work if audit_type is empty. Also, it can fail with
uniqueness violation when doing it inside transactions, like I
described one post above. Would be interesting to know if it can fail
without transactions involved too.

It’s very simple. Just insert the value(s) where 0 equals the count of the value(s) already existing.

INSERT INTO audit_type
SELECT DISTINCT ‘sample’ FROM audit_type WHERE
0 = (SELECT COUNT(audit_type_desc) FROM audit_type WHERE audit_type_desc = ‘sample’)

1. Start process 1 (psql) and process 2 (psql).

2. In both processes, type “\set AUTOCOMMIT on” (this stops psql from
starting implicit transactions).

3. In process 1, type:

begin;
insert into urls(url) values (‘http://www.xaprb.com/blog/‘);

4. In process 2, type:

insert into urls(url)
select ‘http://www.xaprb.com/blog/‘
from mutex
left outer join urls
on urls.url = ‘http://www.xaprb.com/blog/‘
where mutex.i = 1 and urls.url is null;

5. Process 2 hangs waiting for process 1 to commit or roll back.

6. In process 1, type:

commit;

7. Behold error in process 2:

ERROR: duplicate key value violates unique constraint “urls_pkey”

It’s tricky to test this with two processes without a transaction, but
I suspect this can also fail without any transactions involved.

I have the below syntax but it is always insert duplicates can someone please help

INSERT INTO roshcon_vehicle_v1_0
(VehicleRegNumber,VehicleType,VehicleMake,driver_FstName,driver_Surname,driver_TelNr1Number,driver_SubName,driver_TelNr4Number,driver_SubManagerEmail ,Hire_Time)
SELECT roshcon_vehicle_report_001.VehicleRegNumber, VehicleType,VehicleMake,roshcon_vehicle_drivers_v1_0.driver_FstName, roshcon_vehicle_drivers_v1_0.driver_Surname,driver_TelNr1Number,driver_SubName,driver_TelNr4Number,driver_SubManagerEmail , Hire_Time
FROM roshcon_vehicle_driver_v1_0, roshcon_vehicle_report_001, roshcon_vehicle_drivers_v1_0
WHERE roshcon_vehicle_report_001.Vehicle_Id = roshcon_vehicle_driver_v1_0.Id
AND roshcon_vehicle_drivers_v1_0.driver_Id = roshcon_vehicle_driver_v1_0.driver_FstName