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Computer science · lesson 3 of 4

Joins and relationships

An operation combining rows according to a relationship condition.

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Learn the ideas

Prerequisites: Basic computing and simple data tables.

Join

An operation combining rows according to a relationship condition.

One-to-many

A relationship where one row can correspond to several rows in another table.

Inner join

A join returning rows with matches under the join condition.

Left join

A join retaining all rows from the left side plus matching right-side rows.

Worked examples

Example 1

Which term best matches this description: An operation combining rows according to a relationship condition.

Join is the matching concept in this lesson.

Join

Example 2

Which term best matches this description: A relationship where one row can correspond to several rows in another table.

One-to-many is the matching concept in this lesson.

One-to-many

Check your understanding

8 questions

Decimals or fractions are accepted for numeric answers. Proofs and written responses use sample answers and require human marking. This is practice, not a protected examination.

1 Which term best matches this description: An operation combining rows according to a relationship condition.

Show answer and explanation

Join

Join is the matching concept in this lesson.

2 Which term best matches this description: A relationship where one row can correspond to several rows in another table.

Show answer and explanation

One-to-many

One-to-many is the matching concept in this lesson.

3 Which concept would you apply first in a situation where a join returning rows with matches under the join condition.

Show answer and explanation

Inner join

The scenario directly calls for Inner join.

4 Name the concept described as: A join retaining all rows from the left side plus matching right-side rows.

Show answer and explanation

Left join

The intended concept is Left join.

5 Which statement about Join is most accurate?

Show answer and explanation

An operation combining rows according to a relationship condition.

The definition in the lesson notes gives the required condition.

6 Explain one important difference between Join and One-to-many.

Sample answer and marking guidance

Join: An operation combining rows according to a relationship condition. One-to-many: A relationship where one row can correspond to several rows in another table.

Credit a clear distinction using both definitions and an appropriate example if supplied.

7 Give a short example showing how Inner join would be used in practice.

Sample answer and marking guidance

A valid example should demonstrate this idea: A join returning rows with matches under the join condition.

Credit a relevant scenario that applies the concept rather than merely naming it.

8 Summarize why Left join matters in the lesson “Joins and relationships”.

Sample answer and marking guidance

Left join matters because A join retaining all rows from the left side plus matching right-side rows.

Credit the core purpose, scope and any important limitation from the notes.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.