Grade 11 · 4 lessons and a review

Validate, Join and Summarize Records

Use stable keys, reject duplicate identifiers, preserve missing matches and aggregate related rows.

Before you begin

Read tables and unique identifiers; count items; distinguish an empty group from a missing value.

Choose by skill rather than age alone. Read with an adult when useful, revisit a lesson, or explore another grade.

Lesson 1 of 4

Use identifiers rather than row position to combine two tables.

Lesson 2 of 4

Find duplicate identifiers and stop an ambiguous lookup.

Lesson 3 of 4

Match every left-table row by key and explicitly preserve missing matches.

Lesson 4 of 4

Aggregate matched records and retain objects with zero related rows.

After the lessons, try 4 new review cases and a practical task. Each answer has an explanation and a link back to the related lesson.

Guest answers are temporary. Keep your own paper or document; this unit does not certify completion or record a school grade.