? WHERE Clause in Advance Java

? Quick Overview

In Advance Java, the WHERE clause is used with SQL queries inside JDBC to filter records retrieved from a database. It allows Java applications to fetch only the required data instead of entire tables.

? Key Concepts

Used with SELECT, UPDATE, and DELETE statements
Applies conditions to database queries
Works with comparison, logical, and pattern-matching operators
Helps improve performance and security

? Syntax / Theory

The WHERE clause is written after the table name in an SQL query.

? View Code Example

// SQL syntax using WHERE clause
SELECT column1, column2 FROM table_name WHERE condition;

? Code Example (JDBC)

? View Code Example

// Fetch employee details with salary greater than 30000
String query = "SELECT * FROM employees WHERE salary > 30000";

Connection con = DriverManager.getConnection(url, user, password);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);

while (rs.next()) {
    System.out.println(rs.getInt("id") + " " + rs.getString("name"));
}

? Live Output / Explanation

Explanation

Only employee records whose salary is greater than 30000 will be retrieved. Rows that do not satisfy the WHERE condition are ignored by the database.

? Interactive Simulator

Click a button to see how the Java Query filters the database results:

String sql = "SELECT * FROM employees";

ID	Name	Dept	Salary
101	John Doe	HR	45000
102	Jane Smith	IT	60000
103	Robert Brown	Finance	75000
104	Emily Davis	IT	55000
105	Michael Wilson	HR	48000

? Tips & Best Practices

Always use WHERE clause to avoid unnecessary data retrieval
Use PreparedStatement to prevent SQL Injection
Index columns used frequently in WHERE conditions
Avoid using WHERE without conditions in UPDATE or DELETE

? Try It Yourself

Retrieve students whose marks are greater than 60
Use WHERE with AND and OR conditions
Fetch records using LIKE operator
Modify the query using PreparedStatement