ProgramGuruThe PostgreSQL < operator is used to compare whether one expression is less than another. This operator is essential for filtering query results based on a comparison that checks if a specified column or expression is less than a given value.
SELECT columns
FROM table_name
WHERE column < value;
The < operator has the following components:
columns: The columns to be retrieved from the table.table_name: The table from which to retrieve the data.column: The column to be compared.value: The value to compare against.Let's look at some examples of PostgreSQL < operator queries:
SELECT customer_id, customer_name
FROM customers
WHERE customer_id < 3;
This query retrieves the customer_id and customer_name from the customers table where the customer_id is less than 3.
SELECT product_id, product_name
FROM products
WHERE price < 50.00;
This query retrieves the product_id and product_name from the products table where the price is less than 50.00.
SELECT order_id, order_date
FROM orders
WHERE order_date < '2024-01-01';
This query retrieves the order_id and order_date from the orders table where the order_date is earlier than '2024-01-01'.
SELECT customer_id, customer_name
FROM customers
WHERE customer_name < 'M';
This query retrieves the customer_id and customer_name from the customers table where the customer_name is alphabetically less than 'M'.
Let's go through a complete example that includes creating a table, inserting data, and using the Less Than operator to filter data.
This step involves creating a new table named products to store product data.
CREATE TABLE products (
product_id SERIAL PRIMARY KEY,
product_name VARCHAR(100),
price NUMERIC(10, 2)
);
In this example, we create a table named products with columns for product_id, product_name, and price.
This step involves inserting some sample data into the products table.
INSERT INTO products (product_name, price)
VALUES ('Product A', 30.00),
('Product B', 60.00),
('Product C', 90.00);
Here, we insert data into the products table.
This step involves using the < operator to filter data from the products table.
-- Basic Less Than
SELECT product_id, product_name
FROM products
WHERE price < 50.00;
-- Less Than with Numeric Comparison
SELECT product_id, product_name
FROM products
WHERE price < 50.00;
-- Less Than with Date Comparison
SELECT order_id, order_date
FROM orders
WHERE order_date < '2024-01-01';
-- Less Than with String Comparison
SELECT customer_id, customer_name
FROM customers
WHERE customer_name < 'M';
These queries demonstrate how to use the < operator to filter data from the products table, including basic numeric comparisons, date comparisons, and string comparisons.
The PostgreSQL < operator is a fundamental tool for comparing whether one expression is less than another. Understanding how to use the < operator and its syntax is essential for effective data retrieval and manipulation in PostgreSQL databases.