Meet SQL: Your First Query

Write your first SQL query and learn the four things SQL can do.

You know data lives in tables of rows and columns. Now the fun part: asking for it.

Here is a complete, real SQL query:

SELECT * FROM users;

Read it out loud: "Select everything from the users table." That's SQL's superpower — it reads almost like English.

SELECT — "I want to read data"
* — "all the columns"
FROM users — "from the table called users"
; — "end of statement" (like a period ending a sentence)

Run it, and the database hands back every row and every column of the users table.

Predict the output

The users table has 3 rows (Alice, Bob, Carol) and 4 columns. What does this query return?

SELECT * FROM users;

AAll 3 rows with all 4 columns
BJust the first row
CJust the column names, no data
DAn error — you must name the columns

A query like that is called a statement — one complete instruction to the database. The words SELECT and FROM are keywords: SQL's fixed vocabulary. users is a name you chose when creating the table.

Two style rules you'll see everywhere (and should copy):

-- Convention: KEYWORDS in caps, names in lowercase
SELECT * FROM users;

-- SQL itself doesn't care — this works too, but it's harder to read:
select * from users;

SQL keywords are case-insensitive. The UPPERCASE convention exists purely for humans: your eye instantly separates SQL's grammar from your table and column names.

One more nicety:

SQL ignores whitespace — so you can format a query however reads best

Fill in the blank

Complete your first query — read all columns from the products table:

___ * FROM products;

SQL can do four things with data — the famous CRUD operations:

-- C — Create: add new rows
INSERT INTO users (name, email) VALUES ('Dan', 'dan@example.com');

-- R — Read: ask questions (you just did this!)
SELECT * FROM users;

-- U — Update: change existing rows
UPDATE users SET age = 29 WHERE id = 1;

-- D — Delete: remove rows
DELETE FROM users WHERE id = 3;

Don't memorize the last three yet — each gets its own lesson later. Just know the map: INSERT, SELECT, UPDATE, DELETE.

SELECT gets most of your attention — reading data is ~95% of real-world SQL work

Multiple choice

Which SQL operation reads data without changing anything?

ASELECT
BINSERT
CUPDATE
DDELETE

One last big idea before you start querying for real. SQL is declarative: you describe what you want, not how to find it.

In most programming languages you'd write a loop: "go through each user, check the age, add matches to a list…" In SQL you just state the goal:

SELECT * FROM users WHERE age >= 18;

…and the database's query planner figures out the fastest way to get it — which shortcuts to use, what to scan, how to sort. You declare; it optimizes. That's why one line of SQL can replace fifty lines of loop code.

The WHERE age >= 18 bit — your first glimpse of filtering

Multiple choice

What does it mean that SQL is 'declarative'?

AYou describe the result you want; the database decides how to compute it
BYou must declare every variable before using it
CQueries must be written in uppercase
DYou write step-by-step loops over each row

Two style rules you'll see everywhere (and should copy):

-- Convention: KEYWORDS in caps, names in lowercase
SELECT * FROM users;

-- SQL itself doesn't care — this works too, but it's harder to read:
select * from users;

SQL keywords are case-insensitive. The UPPERCASE convention exists purely for humans: your eye instantly separates SQL's grammar from your table and column names.

One more nicety:

SQL ignores whitespace — so you can format a query however reads best

-- C — Create: add new rows INSERT INTO users (name, email) VALUES ('Dan', 'dan@example.com'); -- R — Read: ask questions (you just did this!) SELECT * FROM users; -- U — Update: change existing rows UPDATE users SET age = 29 WHERE id = 1; -- D — Delete: remove rows DELETE FROM users WHERE id = 3;