Databases and SQL

How data is stored, structured and queried, with hands-on SQL against real datasets.

What this course covers

How data is stored, structured and queried, with practice throughout. By the end you can answer your own questions instead of asking someone else and waiting.

SQL is one of the few technical skills where a few days of learning produces an immediate and permanent change in what you can do. It has outlasted every fashion in computing for fifty years, which should tell you something about how solid it is.

What you will learn

• How data is organised into tables, and why that structure matters
• Selecting and filtering, to get exactly the rows you want
• Sorting and limiting results
• Joins, for combining information held in different places
• Grouping and aggregation: counts, totals, averages by category
• Inserting, updating and deleting, safely
• Designing a table sensibly rather than inheriting someone else's mistakes
• The specific traps that make results quietly wrong

Who this is for

• Anyone who currently asks a colleague to pull the numbers
• Staff using reporting tools who want to see behind them
• Developers who can write a query but not an efficient one
• Students taking a database module
• People moving into analyst, administrator or operations roles

You do not need to be a programmer. SQL reads closer to English than most technical things and the start of the curve is gentle. People routinely surprise themselves here.

The mistakes that make answers wrong

Most SQL teaching covers the syntax and stops. The syntax is the easy part. What causes actual damage is the handful of behaviours that produce a query which runs perfectly and returns the wrong answer.

A join that quietly multiplied your rows so every total is inflated. A filter that excluded the records you most needed because of how blanks behave. An average that ignored the missing values instead of counting them. A count that counted something other than what you meant.

These are specific, learnable and rarely taught, and they are the reason people stop trusting their own results. We name each one and show what it looks like when it happens.

Practising on real data

Textbook exercises about imaginary suppliers teach the syntax and nothing about the judgement.

So practice runs against data with the qualities real data has: gaps, duplicates, inconsistent capitalisation, dates stored in more than one way. Learning to notice those and account for them is most of what makes someone reliable with data rather than merely fluent in the language.

Where it leads

Independence, mainly. Being able to answer a question the moment you have it, and enough structural sense to tell when a number looks wrong, which is the skill that matters most and takes longest to acquire elsewhere.

Questions we are often asked

Which database will we use? One where the SQL you learn transfers. The core language is shared across all of them and the differences are minor at this level.

Do I need programming experience? No. This is often someone's first technical course.

Will this help with Excel? It changes how you think about data generally, and the concepts carry across. It is also frequently what convinces people to stop doing certain things in Excel.

Can I use it on our systems at work? That depends on what access you are given, and it is worth asking your organisation before assuming.