If logic in SQL or Access queries - sql

Question

Greetings, fellow SO people.
I am working on a project that has me working with an Access database. Here's the setup:
I have three tables:
Tab1 with employee names, ID#s, Manager names and Manager ID#s.
Tab2 with chat info, employee ID#s and employee names.
Tab3 with Manager ID#s, Manager names and team names.
I currently have a query that selects the following:
tab2.[employee name], tab2.[employee id], tab3.[chat info], tab1.[manager id], tab1.[manager id], tab3.[team name]
where
tab2.[employee id] = tab1.[employee id] and tab2.[manager id] = tab3.[manager id];
What I am trying to accomplish is this: I would like to have a way to put "Unknown" in the "Team" field if the IDs don't match up somewhere along the line. Any ideas?
Thanks in advance!

Answer 1

Perhaps something like:
select tab2.[employee name],
tab2.[employee id],
tab3.[chat info],
tab1.[manager id],
Nz(tab3.[team name], 'Unknown') as [team name]
from (tab2
left join tab1
on tab2.[employee id] = tab1.[employee id])
left join tab3
on tab2.[manager id] = tab3.[manager id]

Answer 2

SELECT
tab2.[employee name], tab2.[employee id],
tab3.[chat info], tab1.[manager id],
tab1.[manager id],
Nz(tab3.[team name],"Unknown")
FROM (tab2
LEFT JOIN tab1
ON tab2.[employee id] = tab1.[employee id])
LEFT JOIN tab3
ON tab2.[manager id] = tab3.[manager id];

Answer 3

It seems that Access doesn't support SQL case statements, so my previous answer is incorrect. I'm leaving it there for anyone looking for the same problem with a SQL compliant database.
Apparently you can use a switch statement to achieve the same result; this example shows how a switch can be used. Hopefully that's more helpful.
Otherwise, if possible, switch to a real DB :)

Answer 4

Okay, I was slow off the mark with the fact that you can't use CASE, and Joe's use of Nz is probably your best bet, but there is another Access-specific alternative, presented here in case it fits your situation better:
select tab2.[employee name],
tab2.[employee id],
tab3.[chat info],
tab1.[manager id],
Iif(IsNull(tab3.[team name]), 'Unknown', tab3.[team name]) as [team name]
from tab2
left join tab1
on tab2.[employee id] = tab1.[employee id]
left join tab3
on tab2.[manager id] = tab3.[manager id]
In this situation, Iif( condition, trueAnswer, falseAnswer ) does the same thing as the Nz, but if your condition is something besides an IsNull it can be more flexible.

Answer 5

I'm not sure about Access, but in SQL normally you would left join your tables and you can use a CASE statement to add the conditional behaviour your looking for; access may not support this.
The example shown here is reasonably standard.
Wow, do access queries really look like that? Hmmm... Then perhaps something like this.
tab2.[employee name], tab2.[employee id], tab3.[chat info], tab1.[manager id], tab1.[manager id], case when tab3.[team name] is null then 'Unknown' else tab3.[team name] end as [team name]
where
tab2.[employee id] = tab1.[employee id] and tab2.[manager id] = tab3.[manager id];