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← Revision deskFree companion · 15 minute suggested activity

SQL: query grain and validation

A short retrieval session. Try the questions before revealing the explanations; revisit them after a few days and again in a later week.

Learn → Try → ExplainReviewed 2026-10-15
01

Recall without looking

What does one result row represent? When does a join amplify rows? Why filter before aggregation?

Check and explain

Result grain must follow the question. A one-to-many join repeats parent values; reconcile counts and sums. WHERE filters source rows, HAVING filters groups.

03

Transfer task

Write monthly completed sales from memory, then compare with the SQL monthly challenge. Change the task to channel share and explain the denominator.

04

Record your next review

Write which concept you missed and one new example. Revisit after 2–3 days, then about a week; adjust the interval to your needs. This is a suggested study routine, not an automated reminder or saved score.

Make the reasoning yours.

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