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Data & Analytics · Intermediate

Schema-on-Read

Applying structure to data when it is queried, rather than enforcing a schema when it is written.

Definition

Schema-on-read gives flexibility for raw, varied data in lakes. Errors surface at query time instead of load time. External tables in Athena, BigQuery and Snowflake use it.

Exam tip

Data lake = schema-on-read; data warehouse = schema-on-write.

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