SQL (Structured Query Language) is used to retrieve, manipulate, and analyze data stored in databases.
1️⃣ Understanding Databases & Tables
Databases store structured data in tables.
Tables contain rows (records) and columns (fields).
Each column has a specific data type (INTEGER, VARCHAR, DATE, etc.).
2️⃣ Basic SQL Commands
Let's start with some fundamental queries:
🔹 SELECT – Retrieve Data
SELECT * FROM employees; -- Fetch all columns from 'employees' table SELECT name, salary FROM employees; -- Fetch specific columns
🔹 WHERE – Filter Data
SELECT * FROM employees WHERE department = 'Sales'; -- Filter by department SELECT * FROM employees WHERE salary > 50000; -- Filter by salary
🔹 ORDER BY – Sort Data
SELECT * FROM employees ORDER BY salary DESC; -- Sort by salary (highest first) SELECT name, hire_date FROM employees ORDER BY hire_date ASC; -- Sort by hire date (oldest first)
🔹 LIMIT – Restrict Number of Results
SELECT * FROM employees LIMIT 5; -- Fetch only 5 rows SELECT * FROM employees WHERE department = 'HR' LIMIT 10; -- Fetch first 10 HR employees
🔹 DISTINCT – Remove Duplicates
SELECT DISTINCT department FROM employees; -- Show unique departments
Mini Task for You: Try to write an SQL query to fetch the top 3 highest-paid employees from an "employees" table.
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