Only the Friday pizza
The canteen manager asks one question: "How many pizzas did we sell on Friday?"
Nobody wants every row of the week. A logical search picks out exactly the rows that answer the question.
Key words
| Word | What it means | Example |
|---|---|---|
| Query | a question you ask a database | |
| Condition | a test that each row passes or fails | day = 'Fri' |
| Logical operator | a word that joins conditions | AND, OR, NOT |
| Parameter | a detail that limits a query, such as a day or a price | |
| Boolean | a value that is only true or false | |
| Database | an organised store of data that you can search |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can write a condition with AND, OR and NOT to find the rows I need.
Starter
Have a go
Starter
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A logical query searches accurately
The purpose of a query is to search for the data you need, and no more. It tests each row against a condition.
A condition gives a Boolean answer: true or false. Only rows where it is true come back.
Try it: one condition
select item, qty
from canteen_sales
where day = 'Fri' and item = 'pizza';
-- Try it: change pizza to wrap.
Check
Have a go
Check
3 questionsHave a go: your answers are marked here and then forgotten. Sign in if you would like your score kept, and to pick up where you left off.Sign in to keep your score
Your answers are marked here and are not kept. A college account keeps every student’s marks.