How can you combine and store data from different sources in an Oracle database?

There are several approaches to combine and store data from various sources in an Oracle database:

1. Using SQL*Loader or external tables — if data comes from files, you can load it using SQL*Loader or create external tables that reference the files.

2. Using PL/SQL and procedures — you can write procedures that combine data from different tables or sources within the database.

3. Using ETL tools (Extract, Transform, Load) — for example, Oracle Data Integrator (ODI) or third-party ETL tools that allow extracting data from different sources, transforming it, and loading it into Oracle.

4. Using Java and JDBC — from a Java application, you can retrieve data from various sources (e.g., REST API, other databases), combine it in memory, and then save it to Oracle via JDBC.

An example of simple data merging from two tables and inserting into a third:

INSERT INTO target_table (id, name, value)
SELECT a.id, a.name, b.value
FROM source_table_a a
JOIN source_table_b b ON a.id = b.id;

If data is from external systems, in Java you can:

// Retrieve data from different sources
List<Data> dataFromSource1 = getDataFromSource1();
List<Data> dataFromSource2 = getDataFromSource2();

// Merge data
List<Data> combinedData = new ArrayList<>();
combinedData.addAll(dataFromSource1);
combinedData.addAll(dataFromSource2);

// Save to Oracle
try (Connection conn = DriverManager.getConnection(dbUrl, user, password)) {
    String sql = "INSERT INTO target_table (id, name, value) VALUES (?, ?, ?)";
    try (PreparedStatement ps = conn.prepareStatement(sql)) {
        for (Data d : combinedData) {
            ps.setInt(1, d.getId());
            ps.setString(2, d.getName());
            ps.setDouble(3, d.getValue());
            ps.addBatch();
        }
        ps.executeBatch();
    }
}

Thus, the choice of method depends on the data sources and integration requirements.