📄 SQL Basics Tutorial – SELECT, WHERE, INSERT, ORDER BY Explained
🧲 Introduction – Why Learn SQL Basics First?
Learning the basics of SQL is the foundation of interacting with relational databases. From retrieving specific records to updating millions of rows, SQL provides a clear, English-like syntax for communicating with your database.
Whether you’re a developer, data analyst, or IT student, mastering SQL basics allows you to:
🔍 Query and filter data quickly
✍️ Modify data reliably
📊 Analyze datasets using built-in functions
This guide covers the most common SQL queries and clauses that form the building blocks of all database operations.
📘 Topics Covered
| 🔖 Clause | 📄 Description |
|---|---|
| 🎯 SQL SELECT | Retrieve specific columns or entire tables |
| 🔍 SQL SELECT DISTINCT | Return only unique (non-duplicate) values |
| 📌 SQL WHERE | Filter results based on conditions |
| 📊 SQL ORDER BY | Sort query output ascending or descending |
| 🧠 SQL AND, OR, NOT | Combine and invert filter conditions |
| ✍️ SQL INSERT INTO | Add new rows into a database |
| 🧺 SQL NULL Values | Handle missing or undefined values |
| 🛠️ SQL UPDATE | Modify existing records |
| 🧹 SQL DELETE | Remove records from a table |
| 🔝 SQL SELECT TOP | Return a limited number of rows |
🎯 1. SQL SELECT – Retrieve Data from Tables
SELECT column1, column2
FROM table_name;
✅ Retrieves data from one or more columns.
💡 Use SELECT * to fetch all columns, but avoid it in production queries.
🔍 2. SQL SELECT DISTINCT – Eliminate Duplicates
SELECT DISTINCT department
FROM employees;
✅ Returns only unique values for the selected column(s).
📌 Helpful when summarizing non-repetitive data.
📌 3. SQL WHERE – Filter Query Results
SELECT * FROM employees
WHERE department = 'Sales';
✅ Filters rows using a condition.
📎 Works with numbers, strings, NULL values, and logical operators.
📊 4. SQL ORDER BY – Sort Results
SELECT name, salary
FROM employees
ORDER BY salary DESC;
✅ Sorts results by one or more columns.
⬆️ Default order is ASC; use DESC for descending.
🧠 5. SQL AND, OR, NOT – Combine Conditions
SELECT * FROM employees
WHERE department = 'Sales' AND salary > 50000;
✅ Use AND and OR to form compound conditions.
🚫 NOT negates the condition.
✍️ 6. SQL INSERT INTO – Add New Records
INSERT INTO employees (name, department)
VALUES ('John Doe', 'Marketing');
✅ Adds a new row to the table.
📝 Ensure column order matches values.
🧺 7. SQL NULL Values – Handle Missing Data
SELECT * FROM employees
WHERE bonus IS NULL;
✅ NULL represents unknown or missing values.
📎 Use IS NULL or IS NOT NULL to filter them.
🛠️ 8. SQL UPDATE – Modify Existing Records
UPDATE employees
SET department = 'Sales'
WHERE id = 3;
✅ Updates data in one or more columns.
⚠️ Always use WHERE to avoid updating all records.
🧹 9. SQL DELETE – Remove Records
DELETE FROM employees
WHERE department = 'HR';
✅ Deletes rows based on a condition.
⚠️ Without a WHERE, all rows will be deleted!
🔝 10. SQL SELECT TOP / LIMIT – Return Top N Results
-- MySQL / PostgreSQL:
SELECT * FROM employees LIMIT 10;
-- SQL Server:
SELECT TOP 10 * FROM employees;
✅ Limits the number of rows returned in the result set.
📌 Use LIMIT in MySQL/PostgreSQL, TOP in SQL Server.
📘 Best Practices for Writing SQL Queries
| ✅ Do This | ❌ Avoid This |
|---|---|
Use SELECT column_names | Avoid SELECT * in production |
Apply WHERE for filtering | Avoid filtering in application code |
| Use proper indentation | Don’t write unformatted long lines |
| Use aliases for clarity | Avoid ambiguous column names |
📌 Summary – Recap & Next Steps
Mastering SQL basics empowers you to retrieve, filter, sort, and group data with confidence. These core queries are used across dashboards, APIs, and business systems.
🔍 Key Takeaways:
- Learn core SQL clauses like
SELECT,WHERE,ORDER BY,GROUP BY,DISTINCT,LIMIT, andINSERT - Use combinations of clauses to form powerful queries
- Format SQL code clearly for better readability and maintenance
⚙️ Real-World Relevance:
These commands power real-time dashboards, data visualizations, user interfaces, and business intelligence systems.
➡️ Next Topic: Learn how to combine multiple tables using SQL Joins.
❓ FAQs – SQL Basics
❓ What is the most basic SQL command?
✅ The SELECT command is the most fundamental SQL statement used to retrieve data.
❓ What’s the difference between WHERE and HAVING?
✅ WHERE filters rows before grouping; HAVING filters groups after aggregation.
❓ How can I remove duplicate results in a query?
✅ Use SELECT DISTINCT to return only unique values.
❓ Can I sort and filter data at the same time?
✅ Yes, combine WHERE and ORDER BY in the same query for sorted and filtered output.
❓ Which databases support LIMIT or TOP?
✅ LIMIT is used in MySQL, PostgreSQL, and SQLite.
✅ TOP is used in SQL Server.
Share Now :
