Access Structured Query Language (SQL) - Access Database Design and Programming - page 91

A 1 A 2 B 1 B 2 B 3 C 1 C 2 C 3

a3 l ink b2 link l ink2 c2 v l ink2

a3 link b2 link link2 c1 t link2

a2 l ink b2 link l ink2 c2 v l ink2

a2 link b2 link link2 c1 t link2

Now let us add the DISTINCTROW keyword and select a single column from just tblA:

SELECT DISTINCTROW A1
FROM
(Temp1 INNER JOIN Temp2 ON Temp1.A2 = Temp2.B2)
INNER JOIN Temp3 ON Temp2.B3 = Temp3.C3;

Now we consider the projection onto the rows of the only return table (tblA):

A 1 A 2

a3 l ink

a3 link

a2 l ink

a2 link

It is clear that the first two rows of this table are the same row of tblA, so they produce
only one row in the final result table. The same holds for the last two rows. Hence, the
result table is:

A 1

a2
a3

Let us now change this by requesting a column from tblC, thus making it a return table as
well:

SELECT DISTINCTROW A1,C1
FROM
(Temp1 INNER JOIN Temp2 ON Temp1.A2 = Temp2.B2)
INNER JOIN Temp3 ON Temp2.B3 = Temp3.C3;

The projection onto return table rows is now:

A 1 A 2 C 1 C 2 C 3

a3 link c 2 v l ink2

a3 link c1 t link2

a2 link c 2 v l ink2

a2 link c1 t link2

These row “pairs” are all distinct. In fact: