MHB Relation between Sets AUFTRAG & KUNDE

[I like Serena]

Do we maybe write :

Expression for 1 :
SELECT KUNDE.kundnr, KUNDE.ort
FROM KUNDE

That is effectively the same as before.

I think it might be:
SELECT k1.kundnr, k2.ort
FROM KUNDE k1, KUNDE k2
:unsure:

So we need in these cases "DISTINCT", right?

In question 2, yes, we can expect that the same customer has multiple orders, so their name will get listed multiple times.
DISTINCT then ensures each name is listed only once.

In question 3 it is not be necessary. Orders are unique. So if we list the AUFTRAGNR's, we will already have at most one of each.

Ah we have to write that this inequality holds for each a in AUTRAG, don't we?

Indeed. (Sweating)

 

[mathmari]

That is effectively the same as before.

I think it might be:
SELECT k1.kundnr, k2.ort
FROM KUNDE k1, KUNDE k2
:unsure:

So that we consider two different columns? :unsure:

In question 2, yes, we can expect that the same customer has multiple orders, so their name will get listed multiple times.
DISTINCT then ensures each name is listed only once.

In question 3 it is not be necessary. Orders are unique. So if we list the AUFTRAGNR's, we will already have at most one of each.

Indeed. (Sweating)

So do we have to write the following ? Expression for 1 :
SELECT k1.kundnr, k2.ort
FROM KUNDE k1, KUNDE k2 Expression for 2 :
SELECT DISTINCT NAME
FROM KUNDE k, AUFTRAG a
WHERE k.KUNDNR = a.KUNDNRExpression for 3 :
SELECT DISTINCT AUFTRAGNR
FROM AUFTRAG a, KUNDE k
WHERE a.KUNDNR = k.KUNDNR AND (k.ORT = Gießen OR k.ORT = Wetzlar)Expression for 4 :
SELECT DISTINCT KUNDNR
FROM KUNDE k
WHERE k.KUNDNR != ALL
$ \ \ \ \ \ $(SELECT KUNDNR
$ \ \ \ \ \ $FROM AUFTRAG)
:unsure:

 

[I like Serena]

Looks right to me. (Nod)