SQL Essentials: Filtering and Sorting Data

1. Filtering Data with WHERE

The WHERE clause is used to filter records based on specific conditions. It allows you to specify which records you want to retrieve.

Here’s an example of using the WHERE clause:

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SELECT * FROM Customers
WHERE Country = 'USA';

This query retrieves all customers located in the USA.

2. Using Operators in WHERE

In addition to basic equality, you can use various operators in the WHERE clause to refine your data selection:

• Comparison Operators: =, <>, <, >, <=, >=
• Logical Operators: AND, OR, NOT

Example:

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SELECT * FROM Customers
WHERE Country = 'USA' AND Age >= 30;

This query retrieves customers from the USA who are 30 years old or older.

3. Sorting Data with ORDER BY

The ORDER BY clause is used to sort the result set in either ascending or descending order.

Here’s how to sort data:

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SELECT * FROM Customers
ORDER BY LastName ASC;

This query sorts the customers by their last names in ascending order. You can use DESC for descending order.

4. Sorting by Multiple Columns

You can also sort data by multiple columns by specifying them in the ORDER BY clause:

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SELECT * FROM Customers
ORDER BY Country ASC, LastName DESC;

This query sorts customers first by country in ascending order, and then by last name in descending order.

5. Combining Filtering and Sorting

You can combine filtering and sorting to refine your results further:

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SELECT * FROM Customers
WHERE Country = 'USA'
ORDER BY LastName ASC;

This query retrieves all customers from the USA and sorts them by last name.

6. Conclusion

Filtering and sorting are vital skills in SQL that allow you to manage and retrieve data efficiently. Mastering these operations will help you interact with databases effectively.