In the context of this exercise, when doing an
INNER JOIN, are columns matched on
No, when you have
NULL values in a column, these are never matched to other
NULL values. This is because
NULL signifies the absence of any value, and cannot be compared as they will never equal anything. Doing say
NULL = NULL results in False.
Let’s take for example the animation given in the exercise, which shows how
INNER JOIN works. Let’s say that an additional row was added to each table, with
NULL in the
C2 column, such that they become
C1, C2 A, B Q, W X, Y T, NULL
C2, C3 B, C E, R Y, Z NULL, V
If we inner joined these tables the same way, we would end up with the same result, because
NULL values are not matched.
C1, C2, C3 A, B, C X, Y, Z