IGCSE Computer Science Paper 2 Definitions Worksheet: 9 Databases (Modules 525–538)
Name:
Date:
Class:
✎
Key terms
Write what each term means, in your own words.
1
SELECT lastName, firstName FROM students;
2
WHERE Town = 'Leeds'
3
WHERE (A OR B) AND C
4
SELECT FROM WHERE ORDER BY
5
SUM(field)
6
COUNT(*)
7
SELECT COUNT(*) FROM Member WHERE Town = 'Leeds';
8
WHERE, ORDER BY, SELECT
9
SELECT field FROM table WHERE condition;
10
SELECT fields FROM table WHERE condition ORDER BY field DESC;
Answer Key
IGCSE Computer Science Paper 2 · Modules 525–538 · Student wording will vary for definitions
1SELECT lastName, firstName FROM students; — The output has only the fields named, as columns in the order written after SELECT, with a heading row of field names and one row per record kept (all records if there is no WHERE).
2WHERE Town = 'Leeds' — The value in a WHERE condition must match the field's data type: text and characters go in quotes, numbers do not, and Boolean fields use TRUE or FALSE, e.g. Member = TRUE.
3WHERE (A OR B) AND C — Brackets make SQL work out the OR first, then the AND. A record must meet C and also A or B. Moving the brackets, as in A OR (B AND C), can return different records.
4SELECT FROM WHERE ORDER BY — The order of clauses in a full SQL query: SELECT, FROM, WHERE, then ORDER BY. WHERE filters the rows first, then ORDER BY sorts the rows that are left.
5SUM(field) — Adds up all the values in a numeric field and returns one total, e.g. SELECT SUM(Score) FROM Results; gives one row. It only works on numbers.
6COUNT(*) — SQL function that counts records. SELECT COUNT(*) FROM Students; outputs one row with the number of records in the table. It counts rows, whereas SUM adds up values.
7SELECT COUNT(*) FROM Member WHERE Town = 'Leeds'; — WHERE filters the records first, then COUNT or SUM works only on the matching ones. This counts members from Leeds. If no record matches, COUNT gives 0.
8WHERE, ORDER BY, SELECT — To find a query's output, first keep the rows that pass WHERE, then sort them with ORDER BY, then show only the SELECT fields or the SUM or COUNT result.
9SELECT field FROM table WHERE condition; — Completing an SQL script: read the task, then fill the gap with the right field, WHERE condition, ASC or DESC, AND or OR, or SUM or COUNT so the query returns exactly what is asked.
10SELECT fields FROM table WHERE condition ORDER BY field DESC; — Turn a request into one SQL statement: pick fields after SELECT, the table after FROM, conditions in WHERE, sort with ORDER BY, and use SUM or COUNT for totals and how many.