Backfill Your SQL Tables Without Breakage Before Anyone Finds Out You Were Wrong

Re-loading missing data will be one of the least glamorous but most important tasks you do as a SQL developer. Get it right.

Zach Quinn

— 8 min read
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Man filling a hole with a shovel.
Backfilling IRL. Photo by Daniel Lincoln on Unsplash.

Why You Need to Backfill Your SQL Tables

Ugh.

Whether I find out from an alerting system or directly from a stakeholder, “ugh” is my natural reaction when I learn that we have missing data.

Like many aspects of data-oriented work, context is what determines whether your missing data is a minor headache or a three-alarm fire.

In any case, identifying and fixing missing data must be a priority of anyone who deals directly with data that is used to guide organizational decision makers because missing, incomplete or error-riddled data can impact both real-time and historical analysis.

To account for these gaps SQL developers (typically data engineers) work through a sometimes-grueling process called backfilling.

If you’re unfamiliar, backfilling is just a catch-all industry term used to describe the CRUD processes involved with correcting incomplete or incorrect data after it should have been loaded.

Since, as a SQL learner, you are mostly working independently with minimal data sources, it is unlikely that you have or will encounter this concept in independent study.

However, being aware of the importance of retroactively correcting anomalies in your tables, you’ll be better positioned to keep your data functioning from day 1.

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