Summary of MySQL WHERE Clause

The WHERE clause is a crucial part of SQL statements that allows you to filter records based on specific conditions. This guide is designed to help beginners understand its purpose, syntax, and practical usage.

Key Concepts

• Purpose: The WHERE clause is used to specify conditions that filter the results of a query. Without it, SQL returns all records from a table.

Syntax:

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Basic Conditions

• Comparison Operators:
  • =: Equal to
  • != or <>: Not equal to
  • >: Greater than
  • <: Less than
  • >=: Greater than or equal to
  • <=: Less than or equal to
• Logical Operators:
  • AND: Combines conditions; both must be true.
  • OR: Combines conditions; at least one must be true.
  • NOT: Negates a condition.

Examples

Negating Conditions with NOT:

SELECT * FROM Customers
WHERE NOT Country = 'USA';

This gets all customers who are not from the USA.

Using OR:

SELECT * FROM Customers
WHERE Country = 'USA' OR Country = 'Canada';

This fetches customers from either the USA or Canada.

Combining Conditions with AND:

SELECT * FROM Customers
WHERE Country = 'USA' AND City = 'New York';

This retrieves customers who are in New York, USA.

Simple WHERE Clause:

SELECT * FROM Customers
WHERE Country = 'USA';

This query selects all customers from the USA.

Conclusion

The WHERE clause is a powerful tool for filtering data in SQL queries. Understanding how to use it effectively allows you to retrieve specific records that meet your criteria, making data management more efficient.