I’ve got an interesting comment the other day saying “I’ve heard Jay Pipes saying indexes with cardinality lower than 30% are worthless, true?” That is interesting question and it has different answers depending on who is asking. A lot of people want to hear simple answers to the questions because they would be overwhelmed by complete answer, it is like children being taught math first taught simple division skills like you can divide 10 by 2 but not by 3.
