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Data & Analytics · Intermediate

Full Table Scan

Reading every row of a table to answer a query, typically because no usable index exists or most rows are needed.

Definition

On large OLTP tables, full scans signal missing indexes or non-sargable predicates. In columnar warehouses, scans are normal, and pruning by partitions or micro-partitions plus column projection limits what is read.

Exam tip

In Snowflake's Query Profile, compare 'Partitions scanned' with 'Partitions total' to see whether pruning worked.

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