🗄️ SQL & Databases

Learn to query databases using SQL - the standard language for working with data!

What you'll learn:

What databases are and why we use them
The SELECT command to retrieve data
The FROM clause to specify which table
The WHERE clause to filter results

What is a Database?

A database is an organised collection of data stored electronically. Think of it like a powerful spreadsheet that can store millions of records and retrieve them instantly!

Example: students table

id	name	age	year_group	house
1	Alice	14	9	Red
2	Bob	15	10	Blue
3	Charlie	14	9	Red
4	Diana	16	11	Green
5	Eve	15	10	Blue

Table: A collection of related data organised in rows and columns (like the students table above)

Record (Row): A single entry in a table (e.g., one student's information)

Field (Column): A specific piece of information (e.g., name, age, house)

What is SQL?

SQL (Structured Query Language) is the standard language for communicating with databases. It lets you:

Retrieve data (SELECT)
Insert new records (INSERT)
Update existing records (UPDATE)
Delete records (DELETE)

SQL is used by almost every website and app you use - from social media to online shopping!

The SELECT Statement

SELECT is the most common SQL command - it retrieves data from a database.

SELECT ... FROM

Choose columns and table

SELECT specifies which columns you want. FROM specifies which table.

SQL Query

SELECT name, age
FROM students;

Result:

name	age
Alice	14
Bob	15
Charlie	14
Diana	16
Eve	15

SELECT * (All Columns)

Get everything

Use * (asterisk) to select ALL columns from a table.

SQL Query

SELECT *
FROM students;

This returns ALL columns: id, name, age, year_group, house

WHERE (Filter Results)

Only matching rows

WHERE filters the results to only include rows that match a condition.

SQL Query

SELECT name, house
FROM students
WHERE house = 'Red';

Result:

name	house
Alice	Red
Charlie	Red

WHERE Comparison Operators

Use these operators in WHERE clauses to filter data:

Operator	Meaning	Example
`=`	Equal to	`WHERE age = 15`
`!=` or `<>`	Not equal to	`WHERE house != 'Red'`
`<`	Less than	`WHERE age < 15`
`>`	Greater than	`WHERE age > 14`
`<=`	Less than or equal	`WHERE year_group <= 10`
`>=`	Greater than or equal	`WHERE age >= 15`

Combining Conditions: AND, OR

Use AND and OR to combine multiple conditions in WHERE.

AND - Both conditions must be true

SELECT name, age, house
FROM students
WHERE age = 14 AND house = 'Red';

name	age	house
Alice	14	Red
Charlie	14	Red

OR - Either condition can be true

SELECT name, house
FROM students
WHERE house = 'Red' OR house = 'Green';

name	house
Alice	Red
Charlie	Red
Diana	Green

SQL Syntax Rules

SQL keywords are NOT case-sensitive

SELECT, select, and Select all work the same. Convention is UPPERCASE.

Text values need quotes

Use single quotes for text: WHERE name = 'Alice'

Numbers don't need quotes

WHERE age = 15 (not '15')

Statements end with semicolon

Always end your SQL statements with ;

Learning Path

Follow these activities in order to master SQL basics.

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1. Predict: Query Results

Predict what data SQL queries will return.

Foundation Not Started

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2. Study: Worked Example

See how to build SQL queries step by step.

Core Not Started

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3. Investigate: Trace Query Execution

Track how SQL processes data step by step.

Core Not Started

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4. Modify: Build SQL Queries

Arrange SQL clauses to create working queries.

Core Not Started

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5. Test: Knowledge Quiz

Check your understanding of SQL basics.

Core Not Started

Key Vocabulary

database

An organised collection of data stored electronically.

table

A collection of related data organised in rows and columns.

record (row)

A single entry in a table containing data for one item.

field (column)

A specific category of data in a table (e.g., name, age).

SQL

Structured Query Language - the standard language for querying databases.

query

A request to retrieve or manipulate data in a database.

SELECT

SQL command to specify which columns to retrieve.

FROM

SQL clause specifying which table to query.

WHERE

SQL clause to filter results based on conditions.

Quick Reference

SQL Quick Reference

-- Select specific columns
SELECT column1, column2 FROM table_name;

-- Select all columns
SELECT * FROM table_name;

-- Filter with WHERE
SELECT * FROM table_name WHERE condition;

-- Multiple conditions with AND
SELECT * FROM students
WHERE age > 14 AND house = 'Blue';

-- Multiple conditions with OR
SELECT * FROM students
WHERE house = 'Red' OR house = 'Blue';