IPA IP 2023 Question 100

A question IPA Japan published in 令和5年度 ITパスポート試験公開問題問100, translated into English. ITPEC is based on the same exams.

Which of the following is the join operation in a relational database?

a)From a table, a table is created by extracting the records that satisfy specific conditions.b)From a table, a table is created by extracting specific fields.c)From two (2) tables, a table is created by extracting the records that have the same values.d)From two (2) tables, a table is created by associating them according to the values of fields.

Explanation

Making one table from two tables, linked by the values of a field — a join combines the rows of two tables that match on a common field.

For example, an “Order” table holds a customer number and a “Customer” table holds the customer number with the customer's name. Joining them where the customer numbers are equal gives one table in which each order carries the customer's name. In SQL this is JOIN … ON or a condition such as Order.CustomerNo = Customer.CustomerNo.

Answer (d)

Why not others:

•(a) — extracting the records (rows) that meet a condition from one table is selection
•(b) — extracting particular fields (columns) from one table is projection
•(c) — taking the records that appear with the same values in both tables is the intersection, a set operation on two tables of the same layout; it relates nothing

Key rule: Selection takes rows, projection takes columns, join links two tables through a shared field; union, intersection and difference are set operations on tables of the same layout.

Databases · AI-written, may contain errors

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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.