What is the difference between ETL and ELT?
Short answer: ETL transforms data before loading it into the warehouse; ELT loads raw data first and transforms it inside the warehouse.
What to cover
- ETL: transform on a separate engine; good for strict compliance or limited warehouse compute.
- ELT: load raw, transform with SQL in the warehouse (dbt); flexible and replayable.
- Cloud warehouses made ELT the default because compute scales cheaply.
Example answer
In ETL we extract, transform on a separate engine like Spark, then load only the cleaned data. In ELT we load raw data straight into the warehouse and transform it there, usually with dbt. ELT is the common choice with Snowflake or BigQuery because the warehouse scales and we can re-run transformations from raw history. ETL still makes sense when data must be masked before it lands.
Avoid
- Claiming ELT is always better — mention the compliance case.
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