How do I use ResultSetMetaData to inspect results?

ResultSetMetaData lets you inspect the shape of a SQL query result at runtime — for example:

• how many columns were returned
• each column’s name and label
• its SQL type
• table/schema info if available
• whether values can be null, are auto-incremented, etc.

Basic usage

package org.kodejava.jdbc;

import java.sql.*;

public class MetaDataExample {
    public static void main(String[] args) throws Exception {
        String url = "jdbc:postgresql://localhost:5432/postgres";
        String user = "postgres";
        String password = "postgres";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             PreparedStatement ps = conn.prepareStatement("SELECT id, name, created_at FROM users");
             ResultSet rs = ps.executeQuery()) {

            ResultSetMetaData meta = rs.getMetaData();
            int columnCount = meta.getColumnCount();

            for (int i = 1; i <= columnCount; i++) {
                System.out.println("Column " + i);
                System.out.println("  Name: " + meta.getColumnName(i));
                System.out.println("  Label: " + meta.getColumnLabel(i));
                System.out.println("  Type: " + meta.getColumnTypeName(i));
                System.out.println("  Java Type: " + meta.getColumnClassName(i));
                System.out.println("  Table: " + meta.getTableName(i));
                System.out.println("  Nullable: " + meta.isNullable(i));
                System.out.println("  Auto Increment: " + meta.isAutoIncrement(i));
            }
        }
    }
}

Common methods

• getColumnCount() — number of columns
• getColumnName(i) — actual database column name
• getColumnLabel(i) — alias from SQL, if present
• getColumnType(i) — JDBC type constant
• getColumnTypeName(i) — database-specific type name
• getColumnClassName(i) — Java class typically used
• getTableName(i) — table name, if the driver provides it
• isNullable(i) — whether the column may contain NULL
• isAutoIncrement(i) — whether it’s auto-generated
• getPrecision(i) / getScale(i) — numeric size details
• isReadOnly(i) — whether the column is read-only

Important note: names vs labels

If your query uses aliases:

SELECT first_name AS name FROM users

Then:

• getColumnName(1) may return first_name
• getColumnLabel(1) returns name

If you want what the query “shows” to the user, prefer getColumnLabel().

Example: print a result set dynamically

try (ResultSet rs = ps.executeQuery()) {
    ResultSetMetaData meta = rs.getMetaData();
    int cols = meta.getColumnCount();

    while (rs.next()) {
        for (int i = 1; i <= cols; i++) {
            String label = meta.getColumnLabel(i);
            Object value = rs.getObject(i);
            System.out.println(label + " = " + value);
        }
        System.out.println("---");
    }
}

Why this is useful

Use ResultSetMetaData when:

• you don’t know the query columns in advance
• you’re building a generic table printer/exporter
• you need to map query results dynamically
• you’re debugging SQL joins or aliases