Beginner SQL: Select Data with Simple Queries

Programming means giving instructions to a computer. SQL (Structured Query Language) is used to interact with databases and obtain information from them efficiently.

Databases are organized systems to store and manage large amounts of data.

First, download a code editor like VS Code or Notepad++. Then install a SQL engine. SQLite is recommended because it's small, free, and works on any computer.

Follow instructions from the official download page for each tool.

To use SQLite, open your terminal and type sqlite3. Inside SQLite, you can write SQL statements to interact with the database.

-- Start SQLite
sqlite3 mydatabase.db

-- Exit SQLite
.exit

Think of a table as a way to organize related data. Each row holds a single item or record, and each column is a property of that item.

-- Example of a table named 'students':
+----+--------+-----+
| id | name   | age |
+----+--------+-----+
| 1  | Alice  | 21  |
| 2  | Bob    | 22  |
+----+--------+-----+

Use the CREATE TABLE command to make a table, then INSERT INTO to add some example records. Run these in your SQL tool.

CREATE TABLE students (
  id INTEGER PRIMARY KEY,
  name TEXT,
  age INTEGER
);

INSERT INTO students (name, age) VALUES ('Alice', 21);
INSERT INTO students (name, age) VALUES ('Bob', 22);
INSERT INTO students (name, age) VALUES ('Carol', 20);

To view all data, use SELECT * FROM followed by the table name. The star (*) means 'all columns'.

SELECT * FROM students;

You should see all rows and columns from the 'students' table.

Type the column names you want after SELECT. Commas separate different columns.

SELECT name, age FROM students;

This will show only the 'name' and 'age' values for each student record.

Add WHERE to your SELECT statement to specify conditions. SQL will return only rows that match.

SELECT * FROM students WHERE age = 21;

You will get only the rows where age is 21.

Try changing the number and operator. For example, to find students older than 20:

SELECT name, age FROM students WHERE age > 20;

To find students named 'Alice' who are older than 20:

SELECT * FROM students WHERE name = 'Alice' AND age > 20;

Or to find students named 'Alice' or anyone aged 22:

SELECT * FROM students WHERE name = 'Alice' OR age = 22;

To list students from youngest to oldest:

SELECT * FROM students ORDER BY age ASC;

To list from oldest to youngest:

SELECT * FROM students ORDER BY age DESC;

Combine LIMIT and ORDER BY to control what and how much you see:

SELECT * FROM students ORDER BY age DESC LIMIT 2;

This shows only the two oldest students in the table.

If you type a column name wrong, you'll see an error. For example:

SELECT nam FROM students;
-- Error: no such column: nam

Make sure every keyword and column name is spelled correctly.

Congratulations! You can now select and filter data with SQL.

Continue by learning to change data (INSERT, UPDATE, DELETE) and advanced topics like combining multiple tables. If you want to show data on a website, consider learning web development alongside SQL.