Question

I am supposed to display drivers who have not been assigned a shift. I have joined the table through the primary key of the driver number. Here’s my code.

select distinct dr_drvname
from driver,shift
where dr_drvnum <> sh_drvnum;

I have made the driver numbers not equal in my code to show the ones not qualified but this code displays all the drivers.

Answer 1

In counterpoint to Justin’s answer, here’s a version using joins:

SELECT d.dr_drvname
FROM driver d
LEFT JOIN shift s
          ON s.sh_drvnum = d.dr_drvnum
WHERE s.sh_drvnum IS NULL

In general, it’s preferable to always explicitly specify your joins, not to use the implicit-join syntax (comma-separated FROM clause).

(but why are you prefixing columns with a -short- table prefix: 'dr_'? Including in the initial table? When you appear to have them prefixed with a slightly longer one anyways: 'drv'?)