sql_basics.md

🎀SQL Basics - SELECT FROM, WHERE, ORDER BY, DISTINCT, LIMIT

📑Table of Contents

1. SELECT FROM
2. WHERE
3. ORDER BY
4. DISTINCT
5. LIMIT

1️⃣ SELECT FROM

This is used to select data from a database.

🔹SELECT specific columns

✏️ Syntax

-- Select query for a specific columns
SELECT column1, column2, ...
FROM table_name;

📝 For example,

SELECT departmentname
FROM departments;

departmentname
Engineering
Sales
HR
Sales
Sales

🔹SELECT *

This is used to return all columns.

✏️ Syntax

-- Select query for all columns
SELECT * 
FROM table_name;

2️⃣ WHERE

This is used to extract only those records that fulfil a specified condition.

✏️ Syntax

--  WHERE query to filter records
SELECT column1, column2, ...
FROM table_name
WHERE condition;

📝 For example,

SELECT *
FROM departments
WHERE departmentname = 'HR';

departmentid	departmentname	location
103	HR	Los Angeles
107	HR	New York
106	HR	New York

3️⃣ ORDER BY

ORDER BY sorts results ascending (ASC) or descending (DESC)

✏️Syntax

-- ORDER BY to sort results
SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;

📝For example,

SELECT *
FROM departments
ORDER BY departmentname;

💡The ORDER BY keyword sorts the records in ascending order by default.

📝For example,

SELECT *
FROM departments
ORDER BY location DESC;

departmentid	departmentname	location
101	Engineering	New York
107	HR	New York
106	HR	New York
109	Engineering	Los Angelos
103	HR	Los Angeles
105	Sales	Los Angelas
104	Sales	Chicago
108	Engineering	Chicago
102	Sales	Chicago

🔹 ORDER BY Several Columns

ORDER BY can sort more than one column.

✏️Syntax

-- ORDER BY to sort several columns
SELECT column1, column2, ...
FROM table
ORDER BY column1 [ASC|DESC], column2 [ASC|DESC], ...;

📝For example,

SELECT *
FROM departments
ORDER BY departmentname ASC, location DESC;

departmentid	departmentname	location
101	Engineering	New York
109	Engineering	Los Angelos
108	Engineering	Chicago
106	HR	New York
107	HR	New York
103	HR	Los Angeles
105	Sales	Los Angelas
102	Sales	Chicago
104	Sales	Chicago

4️⃣ DISTINCT

This is used to return only distinct (different) values, we use SELECT DISTINCT,

✏️ Syntax

-- Select query for all columns
SELECT DISTINCT column1, column2, ...
FROM table_name;

📝 For example,

SELECT DISTINCT location
FROM departments;

location
Chicago
Los Angeles
New York
Los Angelas
Los Angelos

5️⃣ LIMIT

LIMIT restricts the number of rows returned.

📝 For example,

SELECT *
FROM departments
LIMIT 3;

departmentid	departmentname	location
101	Engineering	New York
102	Sales	Chicago
103	HR	Los Angeles