Conceptcardinality estimation / 行数预测
Cardinality Estimation
A core technique in database query optimization that predicts the number of rows returned by a given query condition. It serves as a key input to traditional cost models, and estimation errors in multi-table JOIN scenarios are a primary cause of optimizer performance degradation.
Timeline (last 90 days)
Sep 16
Traditional optimizers typically assume independence among columns during multi-table JOINs, multiplying individual selectivities to estimate result set sizes, while inter-column correlations (such as city and zip code) can cause estimates to differ from actual values by orders of magnitude.
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