Databases & SQL

A database stores tables

• A database keeps data in tables, like a spreadsheet.
• Each row is a record; each column is a field.
• We ask questions in a language called SQL.

SELECT: choose columns

• SELECT picks which columns to show.
• FROM names the table to read.
• * means "all columns".

SELECT name, grade FROM student;

WHERE: filter rows

• WHERE keeps only the rows whose condition is true.
• Put text in single quotes: 'A'.

SELECT name FROM student WHERE grade = 'A';

ORDER BY: sort the results

• ORDER BY sorts the rows by a column.
• Add DESC for largest first, or ASC (the default) for smallest first.

SELECT name, age FROM student ORDER BY age DESC;

In the exam: SQL

• IGCSE uses exactly these clauses: SELECT … FROM … WHERE … ORDER BY.

SELECT Name, Grade
FROM Student
WHERE Grade = 'A';

Common mistakes

• Text values go in single quotes: WHERE name = 'Ann'.
• SELECT chooses the columns; WHERE filters the rows.

Now you try

• Write one SQL query for each task.
• Press Check answer to run it against the table.