SQL Operators and Their Usage

SQL operators are essential components used to perform operations on data in a database. They are used in various SQL statements such as SELECT, INSERT, UPDATE, and DELETE to compare values, perform arithmetic operations, and logically combine conditions. Below is an overview of the key SQL operators and how they are used.

1. Comparison Operators

Comparison operators are used to compare values in SQL statements. These operators allow you to filter and retrieve specific data based on conditions.

Common Comparison Operators:

  • =: Equal to
  • != or <>: Not equal to
  • >: Greater than
  • <: Less than
  • >=: Greater than or equal to
  • <=: Less than or equal to
  • BETWEEN: Range of values
  • IN: Matches any value in a list
  • LIKE: Pattern matching (wildcards)
  • IS NULL: Checks for NULL values
  • IS NOT NULL: Checks for non-NULL values

Example:

SELECT * FROM employees WHERE salary > 50000 AND department = 'Sales';

This query retrieves all employees who earn more than 50,000 and work in the 'Sales' department.

2. Logical Operators

Logical operators allow you to combine multiple conditions in a WHERE clause. These operators evaluate the truth value of one or more conditions.

Common Logical Operators:

  • AND: Returns true if both conditions are true.
  • OR: Returns true if at least one of the conditions is true.
  • NOT: Reverses the result of a condition.

Example:

SELECT first_name, last_name FROM employees WHERE department = 'Sales' AND salary > 50000;

This query will retrieve employees in the 'Sales' department whose salary is greater than 50,000.

3. Arithmetic Operators

Arithmetic operators perform mathematical calculations on data in SQL.

Common Arithmetic Operators:

  • +: Addition
  • -: Subtraction
  • *: Multiplication
  • /: Division
  • %: Modulus (remainder of division)

Example:

SELECT product_name, price, price * 1.1 AS new_price FROM products;

This query calculates a new price for each product by applying a 10% increase.

4. String Operators

String operators allow you to perform operations on string data types such as concatenation and pattern matching.

Common String Operators:

  • ||: Concatenates two strings.
  • LIKE: Pattern matching for strings.
  • %: Wildcard representing zero or more characters in LIKE queries.
  • _: Wildcard representing a single character in LIKE queries.

Example:

SELECT first_name || ' ' || last_name AS full_name FROM employees;

This query concatenates the first_name and last_name columns to create a full_name.

5. Aggregate Operators

Aggregate operators are used to perform calculations on a set of values and return a single result. These operators are commonly used with the GROUP BY clause.

Common Aggregate Operators:

  • COUNT(): Returns the number of rows that match a specified condition.
  • SUM(): Returns the sum of a numeric column.
  • AVG(): Returns the average value of a numeric column.
  • MIN(): Returns the minimum value of a column.
  • MAX(): Returns the maximum value of a column.

Example:

SELECT department, COUNT(*) AS employee_count FROM employees GROUP BY department;

This query returns the number of employees in each department.

6. Set Operators

Set operators allow you to combine the results of multiple queries. These operators return unique results from the combined queries.

Common Set Operators:

  • UNION: Combines the results of two queries, removing duplicates.
  • UNION ALL: Combines the results of two queries, including duplicates.
  • EXCEPT: Returns rows from the first query that do not exist in the second query.

Example:

SELECT employee_id FROM employees_in_sales UNION SELECT employee_id FROM employees_in_marketing;

This query combines the employee IDs from both the 'Sales' and 'Marketing' departments.

7. Existential Operators

Existential operators are used to test for the existence of rows that meet a certain condition.

Common Existential Operators:

  • EXISTS :  Returns true if a subquery returns any rows.
  • NOT EXISTS : Returns true if a subquery returns no rows.

Example:

SELECT first_name, last_name FROM employees WHERE EXISTS (SELECT * FROM sales WHERE employees.employee_id = sales.employee_id);

This query retrieves employees who have made at least one sale, using the EXISTS operator.

8. Null-Related Operators

Null-related operators are used to handle NULL values in SQL.

Common Null-Related Operators:

  • IS NULL: Checks if a value is NULL.
  • IS NOT NULL: Checks if a value is not NULL.

Example:

SELECT first_name, last_name FROM employees WHERE hire_date IS NULL;

This query retrieves employees who do not have a hire date.

Example with IS NOT NULL:

SELECT first_name, last_name FROM employees WHERE hire_date IS NOT NULL;

This query retrieves employees who have a hire date.

9. Using BETWEEN for Range Values

The BETWEEN operator is used to filter the results within a specific range. It is often used with numeric, date, or time values.

Example:

SELECT first_name, last_name, salary FROM employees WHERE salary BETWEEN 40000 AND 70000;

This query retrieves employees whose salary is between 40,000 and 70,000 (inclusive).

Conclusion

SQL operators are fundamental for performing various operations on data in a database. From comparison operators to logical, arithmetic, and aggregate operators, each serves a specific function to help you create flexible and powerful queries. Understanding these operators and how to use them effectively will allow you to retrieve, modify, and analyze data in a more efficient and precise manner.

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