Answer
It predicts row counts for query operations. Accurate estimates help SQL choose the best join and operator strategy.
Quick Answer
Cardinality estimation predicts how many rows each step in a query plan will produce. Wrong estimates lead to wrong join strategies, wrong memory grants, and wrong index choices. The estimator relies on statistics — stale or missing stats cause it to guess badly, which cascades into a poorly-performing plan.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ