Keywords in SQL Explained: Complete Guide with Examples for Beginners

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Structured Query Language (SQL) is the backbone of working with relational databases. Whether you’re retrieving data, modifying records, or managing access, you’ll find that SQL keywords are essential building blocks of any SQL query. 

Understanding what SQL keywords are, how they’re used, and which ones are most common is crucial for anyone learning database programming or working with data.

What Are SQL Keywords? 

SQL keywords are reserved words used to perform specific operations in SQL. These words have special meanings and cannot be used for other purposes, such as naming a column or table. They form the syntax of SQL commands and are used to interact with the database in various ways, like querying, updating, and managing data.

Think of SQL keywords as the "grammar" of SQL that define the structure and meaning of SQL statements.

Importance of SQL Keywords

• They define the structure of your SQL commands.
  
• They ensure consistency across databases and platforms.
  
• They help databases understand your instruction.s
  
• They are non-case-sensitive, meaning SELECT, select, and Select are all treated the same (though uppercase is the convention)

Common SQL Keywords with Descriptions

Here’s a list of some of the most commonly used SQL keywords and what they do:

Tips for Using SQL Keywords

• Always write SQL keywords in uppercase to distinguish them from table and column names.
  
• Avoid using keywords as column or table names. If needed, wrap them in backticks or brackets (e.g., SELECT `order` FROM table).
• Use SQL formatting tools or plugins to highlight keywords for readability.

Reserved Words in SQL

Reserved words are predefined keywords that SQL uses for commands and operations that are part of the language’s syntax. They have special meanings and should not be used for naming tables, columns, or other database objects.

Common Reserved Words in SQL (with Examples)

Identifiers in SQL 

Identifiers in SQL are names used to identify database objects like tables, columns, constraints, databases, etc.

SQL Identifiers Table

Identifiers must be unique within their scope, and if using reserved SQL keywords (like SELECT, ORDER, etc.) as identifiers, enclose them in double quotes or square brackets, depending on the SQL dialect.

Complete SQL Keywords with Code Examples

1. SELECT

By using the SQL keyword 'SELECT', you can retrieve data from a table.

SELECT first_name, last_name FROM employees;

2. FROM

By using the keyword 'FROM', you can specify the table from which to select or delete data.

SELECT * FROM customers;

3. WHERE

The keyword 'WHERE' helps you filter records based on a condition.

SELECT * FROM orders WHERE status = 'shipped';

4. INSERT INTO

The keyword 'INSERT INTO' adds new data to a table.

INSERT INTO products (product_name, price)

VALUES ('Laptop', 1200);

5. UPDATE

The keyword 'UPDATE' is used to modify existing data in a table. 

UPDATE employees

SET salary = 50000

WHERE employee_id = 102;

6. DELETE

When removing records from a table, use the keyword 'DELETE. '

DELETE FROM customers

WHERE customer_id = 5;

7. CREATE TABLE

To create a new table in the database, use the keyword 'CREATE TABLE'.

CREATE TABLE books (

  book_id INT PRIMARY KEY,

  title VARCHAR(100),

  author VARCHAR(100)

);

8. DROP TABLE

To delete a table and all its data, use the keyword 'DROP TABLE'. 

DROP TABLE old_records;

9. ALTER TABLE

The keyword 'ALTER TABLE' is used to modify an existing table (adds columns, changes data types).

ALTER TABLE users

ADD COLUMN birthdate DATE;

10. JOIN (INNER, LEFT, RIGHT, FULL)

The keyword 'JOIN' is used to combine rows from two or more tables based on a related column.

SELECT employees.name, departments.dept_name

FROM employees

INNER JOIN departments ON employees.dept_id = departments.id;

11. GROUP BY

The keyword 'GROUP BY' is used to group rows that share the same value of the specified column(s).

SELECT department, COUNT(*) 

FROM employees

GROUP BY department;

12. ORDER BY

When sorting the results in ascending or descending order, use the keyword 'ORDER BY'.

SELECT name, salary 

FROM employees 

ORDER BY salary DESC;

13. HAVING

The keyword 'HAVING' is used to filter group-level data (used with GROUP BY).

SELECT department, COUNT(*) 

FROM employees

GROUP BY department

HAVING COUNT(*) > 10;

14. DISTINCT

To remove duplicate rows from the result, use the keyword 'DISTINCT'. 

SELECT DISTINCT country FROM customers;

15. AS

The keyword 'AS' renames a column or table with an alias.

SELECT name AS full_name FROM users;

16. LIMIT (MySQL, PostgreSQL)

To limit the number of rows returned, use the keyword 'LIMIT'.

SELECT * FROM articles

LIMIT 5;

17. BETWEEN

To filter values within a specified range, use the keyword 'BETWEEN'.

SELECT * FROM orders

WHERE order_date BETWEEN '2024-01-01' AND '2024-12-31';

18. IN

The keyword 'IN' is used to match any value in a list.

SELECT * FROM users

WHERE country IN ('India', 'USA', 'Canada');

19. IS NULL / IS NOT NULL

The keywords 'IS NULL/IS NOT NULL' are used to check for NULL values.

SELECT * FROM students

WHERE email IS NULL;

20. UNION / UNION ALL

To combine results from two SELECT statements, use the keywords 'UNION/UNION ALL'.

SELECT name FROM teachers

UNION

SELECT name FROM students;

21. EXISTS

The keyword 'EXISTS' checks for the existence of rows in a subquery.

SELECT * FROM customers

WHERE EXISTS (

SELECT * FROM orders WHERE customers.id = orders.customer_id

);

22. CASE

The keyword 'CASE' is used to implement conditional logic.

SELECT name,

CASE 

    WHEN score >= 90 THEN 'A'

    WHEN score >= 75 THEN 'B'

    ELSE 'C'

  END AS grade

FROM exams;

23. DEFAULT

To assign a default value to a column, use the keyword 'DEFAULT. '

CREATE TABLE products (

id INT,

  name VARCHAR(50),

  stock INT DEFAULT 0

);

24. PRIMARY KEY

The keyword 'PRIMARY KEY' uniquely identifies each record.

CREATE TABLE students (

  id INT PRIMARY KEY,

  name VARCHAR(100)

);

25. FOREIGN KEY

To establish a link between tables, use the keyword 'FOREIGN KEY'.

CREATE TABLE orders (

  order_id INT,

  customer_id INT,

  FOREIGN KEY (customer_id) REFERENCES customers(id)

);

Standard & Accurate for General SQL

• Keywords like SELECT, INSERT, UPDATE, DELETE, WHERE, JOIN, GROUP BY, etc., are universal in most RDBMS.
  
• Data types like INT, VARCHAR, and DATE are standard.
  
• Logical structures (CASE, BETWEEN, IN, EXISTS) are accurate.
  

Best Practice Tip

When working on production or exam-level SQL:

• Always confirm the SQL dialect (MySQL, T-SQL, PL/SQL, etc.).
  
• Refer to the official documentation of the RDBMS you’re using.

Popular SQL-Based Database Systems

• MySQL
  
• PostgreSQL
  
• Microsoft SQL Server
  
• Oracle Database
  
• SQLite

Conclusion

SQL keywords are the building blocks of database operations, allowing users to retrieve, modify, manage, and analyze data efficiently. From querying with SELECT and filtering with WHERE to managing tables with CREATE and connecting data using JOIN, these reserved words form the core of SQL. Mastering them is essential for anyone looking to work with databases effectively.

Time for a Short Quiz

Frequently Asked Questions (FAQs)

1. What are SQL keywords?

SQL keywords are reserved words in SQL used to perform specific operations on databases, such as retrieving, inserting, updating, or deleting data. Examples include SELECT, FROM, WHERE, INSERT, and UPDATE.

2. Are SQL keywords case-sensitive?

No, SQL keywords are not case-sensitive. For example, SELECT, select, and SeLeCt are all treated the same. However, writing them in uppercase is a common convention for readability.

3. Can SQL keywords be used as table or column names?

Technically, yes, but it’s not recommended. If needed, you must enclose them in double quotes or square brackets (e.g., "SELECT" or [SELECT]), depending on the SQL dialect.

4. What’s the difference between WHERE and HAVING?

• WHERE filters rows before grouping (used with SELECT, UPDATE, DELETE).
  
• HAVING filters groups after grouping (used with GROUP BY).

5. What are the most commonly used SQL keywords?

Some of the most commonly used are:
SELECT, FROM, WHERE, INSERT, UPDATE, DELETE, JOIN, GROUP BY, ORDER BY.

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