How to use PostgreSQL NOT condition?

The PostgreSQL NOT condition is used to negate a condition or expression. It is used when we want to retrieve all the rows from a table that do not meet a specific condition. In other words, it returns the opposite of the condition specified.

The syntax

Here’s the syntax for using the NOT condition in a PostgreSQL query:

SELECT column1, column2, ...
 FROM table_name
  WHERE NOT condition;

The NOT condition is placed before the condition that we want to negate. Let’s look at some basic examples to understand this concept better:

Suppose we have a table of customers with columns for customer_id, customer_name, and city. We want to find all the customers who are not from New York. Here’s how we can use the NOT condition to create this query:

SELECT customer_id, customer_name, city
 FROM customers
  WHERE NOT city = 'New York';

In this query, we have used the NOT condition to negate the condition that specifies that the city must be ‘New York’. Any row that doesn’t meet this condition will be returned in the result set.

Advanced examples

Now let’s look at some more advanced examples of using the NOT condition in PostgreSQL:

Suppose we have a table of orders with columns for order_id, customer_id, order_date, and order_total. We want to find all orders that were not placed in the month of January. Here’s how we can use the NOT condition to create this query:

SELECT order_id, customer_id, order_date, order_total
FROM orders
WHERE NOT EXTRACT(MONTH FROM order_date) = 1;

In this query, we have used the NOT condition to negate the condition that specifies that the order date must be in the month of January. The EXTRACT function is used to extract the month from the order_date column.

Suppose we have a table of products with columns for product_id, product_name, and price. We want to find all products that are not in the price range of $10 to $20. Here’s how we can use the NOT condition to create this query:

SELECT product_id, product_name, price
FROM products
WHERE NOT price BETWEEN 10 AND 20;

In this query, we have used the NOT condition to negate the condition that specifies that the price must be between $10 and $20.

The BETWEEN operator is used to check if the price is within the specified range.

The PostgreSQL NOT condition is a powerful tool that allows us to filter out rows that do not meet a specific condition. It can be used in combination with other conditions such as AND and OR to create more complex filters.

Compare Not with <>

Sure, let’s look at some more advanced examples of using the NOT condition in PostgreSQL and compare it with the PostgreSQL operator <>.

The PostgreSQL operator <> is used to check if two values are not equal. It returns true if the values are not equal, and false if they are equal. The NOT condition, on the other hand, is used to negate a condition or expression.

Let’s look at an example where we can use either the NOT condition or the <> operator:

Suppose we have a table of customers with columns for customer_id, customer_name, and age.

We want to find all customers who are not 25 years old. Here’s how we can use the NOT condition to create this query:

SELECT customer_id, customer_name, age
FROM customers
WHERE NOT age = 25;

In this query, we have used the NOT condition to negate the condition that specifies that the age must be 25.

Any row that doesn’t meet this condition will be returned in the result set.

Alternatively, we can use the <> operator to achieve the same result:

SELECT customer_id, customer_name, age
FROM customers
WHERE age <> 25;

In this query, we have used the <> operator to check if the age is not equal to 25. Any row that satisfies this condition will be returned in the result set.

Both queries will give us the same result, but using the NOT condition can make the query easier to read and understand.

Now let’s look at some more advanced examples of using the NOT condition in PostgreSQL:

Suppose we have a table of employees with columns for employee_id, employee_name, department, and salary. We want to find all employees who do not work in the sales department and earn more than $50,000 per year. Here’s how we can use the NOT condition to create this query:

SELECT employee_id, employee_name, department, salary
FROM employees
WHERE NOT (department = 'sales' AND salary > 50000);

In this query, we have used the NOT condition to negate the condition that specifies that the department must be sales and the salary must be greater than $50,000. Any row that doesn’t meet this condition will be returned in the result set.

Now let’s compare this with the <> operator. We can rewrite the above query using the <> operator as follows:

SELECT employee_id, employee_name, department, salary
FROM employees
WHERE department <> 'sales' OR salary <= 50000;

In this query, we have used the <> operator to check if the department is not equal to sales, or if the salary is less than or equal to $50,000. Any row that satisfies this condition will be returned in the result set.

Both queries will give us the same result, but using the NOT condition can make the query easier to read and understand, especially when dealing with complex conditions.

In conclusion, both the NOT condition and the <> operator are powerful tools in PostgreSQL that allow us to filter out rows that do not meet a specific condition.

While the <> operator is used to check if two values are not equal, the NOT condition is used to negate a condition or expression. Depending on the complexity of the condition, using the NOT condition can make the query easier to read and understand.