What causes SQL exception? How it can be handled? Explain with example.

An SQLException in Java is thrown when something goes wrong with database access using JDBC (Java Database Connectivity).

🔥 Common causes include:

1. Invalid database URL or credentials.
2. Syntax errors in SQL queries.
3. Trying to access non-existent tables/columns.
4. Network issues between application and DB server.
5. Trying to insert duplicate keys (violating constraints).
6. Forgetting to close connections leading to resource exhaustion.

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✅ How to Handle SQLException in Java

You can handle it using try-catch blocks and examine:

• e.getMessage() → Describes the error.
• e.getErrorCode() → Vendor-specific error code.
• e.getSQLState() → SQL state as per ANSI SQL standard.

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🧪 Example: Handling SQLException

import java.sql.*;

public class SQLExceptionExample {
    public static void main(String[] args) {
        Connection conn = null;

        try {
            // Load JDBC driver (optional in modern Java)
            Class.forName("com.mysql.cj.jdbc.Driver");

            // Connect to database
            conn = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/testdb", "root", "wrongpassword"
            );

            // Execute a query
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM non_existing_table");

        } catch (SQLException e) {
            System.out.println("SQLException occurred!");
            System.out.println("Message: " + e.getMessage());
            System.out.println("SQLState: " + e.getSQLState());
            System.out.println("ErrorCode: " + e.getErrorCode());
        } catch (ClassNotFoundException e) {
            System.out.println("JDBC Driver not found: " + e.getMessage());
        } finally {
            // Close connection
            try {
                if (conn != null) conn.close();
            } catch (SQLException e) {
                System.out.println("Failed to close connection: " + e.getMessage());
            }
        }
    }
}

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✅ Best Practices:

• Always use try-with-resources to auto-close Connection, Statement, and ResultSet.
• Log SQL exceptions properly.
• Avoid revealing full SQL errors to users — use generic messages in production.