ASAmol Shukla

1. What a database is

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Lesson 1 of 21

What is a database? Tables, rows and your first SQL query

No SQL experience needed. Learn what a database, table, row, column and primary key are, then write your first SELECT statement.

85 min 5 min read 19 problems · 0 solved No tables needed

In short

What is a database and what is SQL?

A database is an organised store of data kept in tables: each table lists one kind of thing, each row is one record and each column is one fact about it. SQL (Structured Query Language) is the language you use to ask the database questions. MySQL is a database server that understands SQL.

By the end of this lesson you can

  • Explain database, table, row, column and primary key with a real example
  • Tell the difference between MySQL (the server), SQL (the language) and Workbench (the editor)
  • Write SELECT statements that show numbers, text and calculations with clear column names
  • Say what NULL means and why 5 + NULL is NULL

What is a database?

Think of a small shop that keeps its records in a notebook. One page lists customers, another lists products, and a third lists every order. As the shop grows, the notebook becomes hard to search: How many notebooks did we sell in February? Which customer has not ordered yet?

A database is that notebook, organised so a computer can answer such questions in milliseconds. Data lives in tables:

product_id product_name category price
1 Notebook Stationery 100.00
2 Pen Stationery 20.00
3 Desk lamp Electronics 800.00
  • A table holds one kind of thing — here, products.
  • A row (also called a record) is one product: Notebook, Stationery, 100.00.
  • A column (a field) is one fact that every row has: price.
  • A primary key is a column whose value is unique for every row — product_id. Two products could share a name, but never an id.

A database that stores data in related tables like this is a relational database. MySQL, PostgreSQL, SQL Server and Oracle are all relational databases, and the SQL you learn here transfers to all of them with small changes.

MySQL, SQL and Workbench: three different things

Beginners often mix these up, so let us separate them now:

  1. MySQL Server is the program that stores the tables and runs your queries. It runs quietly in the background (on your laptop, a company server or the cloud).
  2. SQL is the language. You write a sentence such as SELECT product_name FROM products; and the server answers with a grid of results.
  3. MySQL Workbench is an editor: a window where you type SQL, press Run, and see the results. Other editors (DBeaver, the command line, this page's practice editor) do the same job.

You do not need Python or any other programming language. SQL is a language of its own, and it reads almost like English.

Your first SQL statement: SELECT

SELECT means show me. It is the most used word in SQL and it never changes stored data, so you cannot break anything with it. The smallest possible query asks MySQL to show a value:

SQL · no tables
SELECT 1 AS first_result;
MySQL result1 row
first_result
1

Read it as: show the number 1 and name the output column first_result. The word AS gives the column a name, called an alias. The semicolon ; ends the statement, like a full stop ends a sentence.

Text, numbers and column names

Numbers are written as they are. Text must be in single quotes — without quotes MySQL thinks the word is a column name. You can show several columns by separating them with commas:

SQL · no tables
SELECT 'Learning Shop' AS shop, 'Pune' AS city, 2026 AS year;
MySQL result1 row
shopcityyear
Learning ShopPune2026

If you want a space inside a column name, wrap the alias in backticks: SELECT 100 AS `unit price`;. Most teams avoid spaces and use snake_case names such as unit_price.

Calculations and the order of operations

SQL can calculate directly. It uses + - * / and follows normal maths rules: multiplication and division happen before addition and subtraction. Brackets change the order.

SQL · no tables
SELECT 2 + 3 * 4 AS answer, (2 + 3) * 4 AS with_brackets, 250 * 0.9 AS sale_price;
MySQL result1 row
answerwith_bracketssale_price
1420225.0

In MySQL, / always gives a decimal result (7 / 2 is 3.5000). Later you will use the same arithmetic on columns, for example quantity * unit_price to get a line total.

NULL: the value that means “unknown”

Sometimes a fact is missing — a customer who never gave an email address. SQL stores this as NULL. NULL is not zero and not an empty text; it means we do not know. Anything calculated from an unknown value is also unknown:

SQL · no tables
SELECT NULL AS missing_value, 5 + NULL AS still_unknown, 0 AS zero_is_a_value;
MySQL result1 row
missing_valuestill_unknownzero_is_a_value
NULLNULL0

You will meet NULL again in lesson 4 (finding rows where a value is missing) and lesson 6 (replacing NULL with a default using COALESCE).

How MySQL reads a statement

  • Keywords are not case-sensitive. select, SELECT and Select are the same. This course writes keywords in capitals so they stand out.
  • Spaces and new lines do not matter. Split long queries over several lines so they are easy to read.
  • Comments are ignored. -- like this comments out the rest of a line; /* like this */ can span lines. Use comments to explain why a query exists.
  • One statement ends at the semicolon. You can put several statements in one script; each gives its own result.
SQL · no tables
-- receipt preview for one item
SELECT
  'Pen' AS item,
  5 AS qty,
  20 AS price,
  5 * 20 AS line_total;
MySQL result1 row
itemqtypriceline_total
Pen520100

Common mistakes

Wrong

SELECT Hello;

Fix

SELECT 'Hello';

Why: Without quotes MySQL looks for a column named Hello and fails with error 1054 (Unknown column).

Wrong

SELECT 100 AS unit price;

Fix

SELECT 100 AS unit_price;  -- or AS `unit price`

Why: The space ends the alias, so MySQL sees an extra word and raises a syntax error (1064).

Wrong

Treating NULL as 0

Fix

Keep NULL in mind whenever data can be missing; lesson 6 shows COALESCE(value, 0).

Why: NULL means unknown, so 5 + NULL is NULL, not 5.

Check yourself

  1. In the products table, what is one row and what is one column?
  2. Why must product_id be unique, while product_name does not have to be?
  3. What does SELECT 2 + 3 * 4 return, and why not 20?

Answer out loud or in your notebook. If one is hard, reread that section before practising.

Frequently asked questions

Do I need to know programming before learning SQL?

No. SQL is its own language and reads close to English. This course assumes no programming or database experience.

Is MySQL free?

Yes. MySQL Community Server and MySQL Workbench are free to download for Windows, macOS and Linux. You can also practise on this page without installing anything.

What is the difference between SQL and MySQL?

SQL is the language for asking questions of relational databases. MySQL is one database server that understands SQL; PostgreSQL, SQL Server and SQLite are others.

Quick quiz — 4 questions

Quick Check: What a database is

1 / 4
In a products table, what is one row?

Answers — What a database is

  1. Easy. Show the number 2 with the column name my_number. Target: One row, my_number = 2. No tables required.

    SELECT 2 AS my_number;

  2. Medium. Ask MySQL to add 2 and 3. Target: One column named total containing 5.

    SELECT 2 + 3 AS total;

  3. Hard. Display your shop's name as text. Target: One column named shop containing Learning Shop. Text needs single quotes.

    SELECT 'Learning Shop' AS shop;

  4. Professional. Prepare a two-column welcome result for your practice notebook. Target: One row: shop = Learning Shop, next_step = Connect MySQL. This is a small handoff task, not an advanced database exercise.

    SELECT 'Learning Shop' AS shop, 'Connect MySQL' AS next_step;

  5. Easy. Show the number 10 in a column called ten. Target: 1 row: ten = 10

    SELECT 10 AS ten;

  6. Easy. Show the word Hello in a column called greeting. Target: 1 row: greeting = Hello

    SELECT 'Hello' AS greeting;

  7. Easy. Multiply 12 by 5 and call it result. Target: 1 row: result = 60

    SELECT 12 * 5 AS result;

  8. Easy. Show 100 minus 35 as change_due. Target: 1 row: change_due = 65

    SELECT 100 - 35 AS change_due;

  9. Medium. Show three columns in one row: a = 1, b = 2, c = 3. Target: 1 row: a = 1, b = 2, c = 3

    SELECT 1 AS a, 2 AS b, 3 AS c;

  10. Medium. A notebook costs 100. Show the price of 3 notebooks as total. Target: 1 row: total = 300

    SELECT 3 * 100 AS total;

  11. Medium. Show the price of a 250 mug after 10% discount as sale_price. Target: 1 row: sale_price = 225.0

    SELECT 250 * 0.9 AS sale_price;

  12. Medium. Show the shop name and city in one row: Learning Shop, Pune. Target: 1 row: shop = Learning Shop, city = Pune

    SELECT 'Learning Shop' AS shop, 'Pune' AS city;

  13. Medium. Calculate 2 + 3 * 4 and explain why the answer is not 20. Target: 1 row: answer = 14

    SELECT 2 + 3 * 4 AS answer;

  14. Hard. Force the addition to happen first: (2 + 3) * 4. Target: 1 row: answer = 20

    SELECT (2 + 3) * 4 AS answer;

  15. Hard. Show a column name that has a space in it: unit price = 100. Target: 1 row: unit price = 100 (backticks keep the space in the name)

    SELECT 100 AS `unit price`;

  16. Hard. Show NULL with the alias missing_value and explain what NULL means. Target: 1 row: missing_value = NULL

    SELECT NULL AS missing_value;

  17. Hard. Show what 5 + NULL returns. Target: 1 row: result = NULL

    SELECT 5 + NULL AS result;

  18. Professional. Create a one-row receipt preview: item Pen, qty 5, price 20, line_total. Target: 1 row: item = Pen, qty = 5, price = 20, line_total = 100

    SELECT 'Pen' AS item, 5 AS qty, 20 AS price, 5 * 20 AS line_total;

  19. Professional. Write the same query twice: once on one line, once split over four lines with a -- comment. Both must give the same result. Target: 1 row: item = Pen, line_total = 100

    /* receipt preview */ SELECT 'Pen' AS item, 5 * 20 AS line_total;

Up next · Lesson 2

Install MySQL and connect

80 min · 19 practice problems

Start next lesson
Install MySQL and connect