Cardinality Estimation
The database optimizer's prediction of how many rows an operator or predicate will produce, which strongly influences plan selection.
Database Context
Cardinality estimation predicts how many rows a predicate or relational operator will produce. Histograms, distinct-value statistics, correlations, and selectivity estimates feed join-order and access-path costing, so large estimation errors can lead directly to poor execution plans.
Estimation Boundary
Knowing the total row count is not enough. Correlated columns, skewed distributions, combined predicates, and stale statistics make real cardinality substantially harder to estimate than a uniform model suggests.
Related Database Concepts
- Execution Plan
- Index Selectivity
- Histogram
- Query Optimizer