Key Terms and Concepts
✓ Predicate— an expression that evaluates to true, false, or unknown.
✓ Cardinality— strictly speaking, refers to the number of unique values in a table. Because SQL Server allows tables to have duplicate rows and indexes to have duplicate key values, cardinality often more generally refers to the number of rows in a table or the number of rows returned by a query plan operator when discussed from a SQL Server perspective. Cardinality can also refer to the number of unique values in an index.
✓ Density— refers to the uniqueness of values within a data set. An index's density is computed by dividing the number of rows that would correspond to a given key value by the number of rows in the table.
✓ Selectivity— a measure ...
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