Sql Between In Like Is Null Complete Guide

1. How does the BETWEEN operator work in SQL?

Answer: The BETWEEN operator is used to filter the result set within a certain range. The values can be numbers, text, or dates. It includes the boundary values unless excluded with NOT BETWEEN. Syntax:

SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

Example:

SELECT *
FROM employees
WHERE salary BETWEEN 30000 AND 50000;

This query retrieves all employees whose salaries are between $30,000 and $50,000, inclusive.

2. Can the BETWEEN operator be used with dates?

Answer: Yes, the BETWEEN operator can be used with dates. It is commonly used to filter results within a date range. Ensure the date format matches the database requirements. Example:

SELECT *
FROM orders
WHERE order_date BETWEEN '2023-01-01' AND '2023-12-31';

This query will fetch all orders placed in the year 2023.

3. What is the difference between BETWEEN and <=, >=?

Answer: The BETWEEN operator includes the boundary values, whereas using <= and >= does the same thing but requires manually specifying both conditions. BETWEEN is more concise and easier to write. Example:

SELECT *
FROM employees
WHERE salary BETWEEN 30000 AND 50000;

-- Equivalent query using <=, >=
SELECT *
FROM employees
WHERE salary >= 30000 AND salary <= 50000;

Both queries return the same result set.

4. How does the IN operator function in SQL?

Answer: The IN operator allows you to specify multiple values in a WHERE clause. It is used to match any of the values in a subquery or a list of values. Example:

SELECT *
FROM employees
WHERE department IN ('HR', 'IT', 'Finance');

This query fetches all employees from the departments HR, IT, and Finance.

5. Can the IN operator be used with subqueries?

Answer: Yes, the IN operator can be used with subqueries, which can return values from another table or calculation. Example:

SELECT *
FROM orders
WHERE customer_id IN (SELECT customer_id FROM customers WHERE country = 'USA');

This query retrieves all orders placed by customers from the USA.

6. How is the LIKE operator used in SQL?

Answer: The LIKE operator is used for pattern matching, and is very useful for searching within strings. It is often used with the wildcard % and _ characters.

• % represents zero or more characters.
• _ represents a single character. Example:

SELECT *
FROM customers
WHERE last_name LIKE 'S%';  -- All last names starting with 'S'
SELECT *
FROM customers
WHERE first_name LIKE 'J_n';  -- All first names starting with 'J', followed by any character, and ending with 'n'

7. What is the difference between '%' and '_' in the LIKE operator?

Answer: The % wildcard matches zero or more characters, while the _ wildcard matches exactly one character. Example:

SELECT *
FROM products
WHERE product_name LIKE 'W_'    -- Matches any product name starting with 'W' followed by exactly one character (e.g., Wax)
SELECT *
FROM products
WHERE product_name LIKE 'W%'    -- Matches any product name starting with 'W' (e.g., Wax, Widget, Widgetry)

8. How does the IS NULL operator work in SQL?

Answer: The IS NULL operator is used to filter records with a NULL value in a specified column. It is important because NULL represents the absence of any value. Example:

SELECT *
FROM employees
WHERE commission_pct IS NULL;

This query retrieves all employees who do not receive a commission.

9. Can IS NULL be combined with other conditions?

Answer: Yes, the IS NULL operator can be combined with other conditions using the AND or OR logical operators. Example:

SELECT *
FROM employees
WHERE department_id IS NULL AND salary > 30000;

This query fetches employees who are not assigned to any department and earn more than $30,000.

10. What is the difference between IS NULL and = NULL in SQL?

Answer: In SQL, you cannot use the equality operator = to check for NULL values. The correct operator for checking NULL values is IS NULL. The expression column = NULL will always evaluate to FALSE because NULL does not equal anything, not even another NULL. Example:

SELECT *
FROM employees
WHERE commission_pct IS NULL;  -- Correct way
SELECT *
FROM employees
WHERE commission_pct = NULL;  -- Incorrect way

The first query will return the desired results, while the second will return zero rows.