Hello guys,

I have some questions about indexes.

From discussions in this list we know that creating FK on a field with
low selectivity (e.g. a lookup table) is a bad thing. That's OK.

But, what about the lookup table itself? Do you think we must skip the
PK on the lookup table either (I am not very happy with this).

What is the reasonable number of rows after which we can safely create
a FK to reference the lookup. For example we have a hierarchy with
about 100 elements. Is it safe to create a FK referencing this
hierarchy?

Generally how do I know that a selectivity is OK. I have an index in another table
with six rows each one with different row ID and the selectivity is
0,1666.. is it bad or good to have this index?

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Best regards,
Alexander mailto:saho@...