•More on averages
–Recall Chap 3. – semi-additive measures require averages
•Bank Account Balances are not additive over time
•Basket counts are not additive across products
–Averages are a ratio; non-additive
–Average = sum of a qty / cardinality
–SQL’s Average function often gets the cardinality wrong; therefore, averages are best constructed by retrieving the sum and cardinality components, then calculating the ratio.
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