sql operators clauses

Syntax:

SELECT column1, column2, ...  
FROM table_name;

Example:

Retrieve the names and ages of all employees from the employees table.

SELECT name, age  
FROM employees;

2. FROM Clause

The FROM clause indicates the table from which data will be fetched. It follows the SELECT clause.

Syntax:

SELECT column1, column2  
FROM table_name;

Example:

Retrieve all records from the products table.

SELECT *  
FROM products;

3. WHERE Clause

The WHERE clause filters records based on specific conditions.

Syntax:

SELECT column1, column2  
FROM table_name  
WHERE condition;

Example:

Fetch employees older than 30.

SELECT name, age  
FROM employees  
WHERE age > 30;

4. ORDER BY Clause

The ORDER BY clause arranges results in ascending or descending order.

Syntax:

SELECT column1, column2  
FROM table_name  
ORDER BY column1 ASC|DESC;

Example:

Sort employees by salary in descending order.

SELECT name, salary  
FROM employees  
ORDER BY salary DESC;

5. GROUP BY Clause

The GROUP BY clause groups rows with identical values in specified columns. It is often used with aggregate functions.

Syntax:

SELECT column_name, aggregate_function(column_name)  
FROM table_name  
GROUP BY column_name;

Example:

Find the total sales per product category.

SELECT category, SUM(sales)  
FROM products  
GROUP BY category;

6. HAVING Clause

The HAVING clause filters grouped results, unlike WHERE, which filters individual rows.

Syntax:

SELECT column_name, aggregate_function(column_name)  
FROM table_name  
GROUP BY column_name  
HAVING condition;

Example:

Show categories where total sales exceed 10,000.

SELECT category, SUM(sales)  
FROM products  
GROUP BY category  
HAVING SUM(sales) > 10000;

7. JOIN Clause

The JOIN clause combines records from multiple tables based on a related column.

Syntax:

SELECT table1.column1, table2.column2  
FROM table1  
JOIN table2  
ON table1.common_column = table2.common_column;

Example:

Retrieve customer orders by joining customers and orders.

SELECT customers.name, orders.order_date  
FROM customers  
JOIN orders  
ON customers.customer_id = orders.customer_id;

8. LIMIT Clause

The LIMIT clause restricts the number of records returned.

Syntax:

SELECT column1, column2  
FROM table_name  
LIMIT number;

Example:

Fetch the first five employees.

SELECT *  
FROM employees  
LIMIT 5;

9. DISTINCT Clause

The DISTINCT clause removes duplicate records from the result set.

Syntax:

SELECT DISTINCT column_name  
FROM table_name;

Example:

Retrieve unique job titles from the employees table.

SELECT DISTINCT job_title  
FROM employees;

10. UNION Clause

The UNION clause combines results from multiple queries, removing duplicates.

Syntax:

SELECT column1 FROM table1  
UNION  
SELECT column1 FROM table2;

Example:

Combine customer lists from two regions.

SELECT name FROM customers_region1  
UNION  
SELECT name FROM customers_region2;