Java for beginners

🚀 **Day 29: Basic Database Interaction (JDBC)!** 🚀

Ever wondered how Java applications store and retrieve data from databases? Today's the day we demystify it with **JDBC (Java Database Connectivity)**! 🤯

JDBC is the standard API for Java to interact with relational databases. We'll cover the fundamental steps: establishing a `Connection`, creating `Statement`s to execute SQL queries, and processing the `ResultSet`. Get ready to make your Java apps data-driven! Let's connect! 🔗

```java
import java.sql.*;

public class SimpleJdbcApp {

// H2 In-Memory Database URL - simple, no separate server needed!
private static final String DB_URL = "jdbc:h2:mem:testdb";
private static final String USER = "sa"; // Default H2 user
private static final String PASS = ""; // Default H2 password (empty for H2 in-memory)

public static void main(String[] args) {
System.out.println("🚀 Day 29: Basic JDBC Interaction! 🚀");
System.out.println("Connecting to H2 In-Memory database...");

// Using try-with-resources ensures Connection and Statement are closed automatically
try (Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
Statement stmt = conn.createStatement()) {

System.out.println("✅ Database connected successfully!");

// 1. Create a table
String createTableSQL = "CREATE TABLE STUDENTS " +
"(id INT PRIMARY KEY AUTO_INCREMENT, " +
"name VARCHAR(255) NOT NULL, " +
"age INT)";
stmt.executeUpdate(createTableSQL); // executeUpdate for DDL (CREATE, ALTER, DROP) and DML (INSERT, UPDATE, DELETE)
System.out.println("✨ Table 'STUDENTS' created.");

// 2. Insert some data
String insertSQL1 = "INSERT INTO STUDENTS (name, age) VALUES ('Alice', 20)";
stmt.executeUpdate(insertSQL1);
String insertSQL2 = "INSERT INTO STUDENTS (name, age) VALUES ('Bob', 22)";
stmt.executeUpdate(insertSQL2);
System.out.println("➕ Data inserted into STUDENTS table.");

// 3. Select and retrieve data
String selectSQL = "SELECT id, name, age FROM STUDENTS";
System.out.println("n--- Retrieving Student List ---");

// Using try-with-resources for ResultSet too, ensures it's closed
try (ResultSet rs = stmt.executeQuery(selectSQL)) { // executeQuery for SELECT statements
while (rs.next()) {
// Retrieve by column name
int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");

// Display values
System.out.println("ID: " + id + ", Name: " + name + ", Age: " + age);
}
} // ResultSet 'rs' is closed here automatically

} catch (SQLException e) {
System.err.println("❌ An SQL error occurred: " + e.getMessage());
// In a real application, you'd log this more robustly
e.printStackTrace();
} finally {
System.out.println("n💡 Database interaction complete. H2 In-Memory database is ephemeral (data is lost when app closes).");
}
}
}
```

Output example:
```
🚀 Day 29: Basic JDBC Interaction! 🚀
Connecting to H2 In-Memory database...
✅ Database connected successfully!
✨ Table 'STUDENTS' created.
➕ Data inserted into STUDENTS table.

--- Retrieving Student List ---
ID: 1, Name: Alice, Age: 20
ID: 2, Name: Bob, Age: 22

💡 Database interaction complete. H2 In-Memory database is ephemeral (data is lost when app closes).
```

**Small Challenge:** 💪 Can you add a new student and then write a `SELECT` query to retrieve *only* students older than 21? (Hint: Use `executeUpdate()` for the new student and add a `WHERE` clause to your `SELECT` query! For example: `SELECT ... FROM STUDENTS WHERE age > 21`).

---

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