Welcome back to our SQL learning journey! In this post, we’re going to explore the essential techniques of filtering and sorting data in SQL. These capabilities are crucial for refining your queries and extracting the precise information you need from your databases.

Using SQL Comparison Operators

When retrieving data from a database, we often want to apply conditions to filter the results based on specific criteria. SQL provides a range of comparison operators that allow us to express these conditions. Here are some commonly used comparison operators:

• = (Equal to)
• <> or != (Not equal to)
• < (Less than)
• > (Greater than)
• <= (Less than or equal to)
• >= (Greater than or equal to)

For example, consider the following query:

SELECT * FROM employees WHERE age > 30;

This query retrieves all columns from the “employees” table where the “age” column is greater than 30.

Combining Conditions with Logical Operators

In SQL, we can combine multiple conditions using logical operators such as AND, OR, and NOT. These operators allow us to create more complex filtering criteria. For example:

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

This query retrieves all columns from the “employees” table where the department is ‘IT’ and the salary is greater than 50000.

Sorting Data with ORDER BY Clause

The ORDER BY clause is used to sort the result set based on one or more columns. By default, the sorting is done in ascending order, but you can specify descending order using the DESC keyword. For example:

SELECT * FROM employees ORDER BY salary DESC;

This query retrieves all columns from the “employees” table and sorts the results in descending order based on the “salary” column.

Handling NULL Values

In SQL, NULL represents the absence of a value. When querying data, it’s essential to consider how NULL values should be treated. You can use the IS NULL and IS NOT NULL operators to filter rows based on whether a column contains a NULL value or not. For example:

SELECT * FROM employees WHERE manager_id IS NULL;

This query retrieves all columns from the “employees” table where the “manager_id” column is NULL.

Summary

In this post, we’ve explored the essential techniques of filtering and sorting data in SQL. We’ve learned how to use comparison operators to filter rows based on specific criteria, combine conditions using logical operators, sort data using the ORDER BY clause, and handle NULL values effectively.

Mastering these techniques will enable you to write more precise and efficient SQL queries, allowing you to extract valuable insights from your databases. In the next post, we’ll delve into aggregate functions and grouping data, exploring how to perform calculations and analyze data at a higher level. Stay tuned for more SQL adventures! If you have any questions or topics you’d like us to cover, feel free to leave a comment below. Happy querying!

Cheers!

J

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