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Normalisation and Structured Query Language

SQL statements for retrieving data

  • 3 things to know
  • A2 Unit 1

Overview

Selecting columns and filtering rows, ordering the result, pattern matching, combining conditions, ranges and lists, the aggregate functions, and removing duplicates.

What you need to know

Answer each one before you reveal it.

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Key term

Why is naming the columns preferred to using an asterisk in an application?

Key term

Write the SQL to list every column of every row in the Member table.

Numbers

Write the SQL to list the surnames of members who joined after the first of January 2026.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Write the SQL to list every column of every row in the Member table.

    Model answer

    The statement is SELECT * FROM Member; where the asterisk stands for every column and the absence of a WHERE clause means every row.

  2. 2

    Why is naming the columns preferred to using an asterisk in an application?

    Model answer

    Naming the columns means the result does not change if a column is added to the table, only the data actually needed is transferred, and a reader of the code can see what the query returns.

  3. 3

    Write the SQL to list the surnames of members who joined after the first of January 2026.

    Model answer

    The statement is SELECT Surname FROM Member WHERE JoinDate > '2026-01-01'; which returns one column and only those rows meeting the condition.

  4. 4

    What does the ORDER BY clause do?

    Model answer

    ORDER BY sorts the rows returned, ascending by default and descending when DESC is added, without changing how the rows are stored. Several columns may be given, the later ones breaking ties in the earlier.

  5. 5

    Write the SQL to list members in surname order, latest joiners first within each surname.

    Model answer

    The statement is SELECT * FROM Member ORDER BY Surname ASC, JoinDate DESC; where the second sort column decides the order within each group of equal surnames.

  6. 6

    What does the LIKE operator do?

    Model answer

    LIKE matches a text value against a pattern, in which the percent sign stands for any sequence of characters and the underscore for exactly one, so LIKE 'Mc%' finds every surname beginning Mc.

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