-- Get the top-3 busiest train stations
SELECT station_name, count(*) AS num_services
FROM train_services
GROUP BY ALL
ORDER BY num_services DESC
LIMIT 3;

-- Load CSV file, auto-detecting column name and types
CREATE TABLE stations AS
FROM 'https://blobs.duckdb.org/stations.csv';

-- Directly query Parquet file in S3
SELECT station_name, count(*) AS num_services
FROM 's3://duckdb-blobs/train_services.parquet'
GROUP BY ALL
ORDER BY num_services DESC
LIMIT 10;

-- Find the top-3 longest domestic train routes
SELECT s1.name_short, s2.name_short, distances.distance
FROM distances
JOIN stations s1 ON distances.station1 = s1.code
JOIN stations s2 ON distances.station2 = s2.code
WHERE s1.country = s2.country
  AND s1.code < s2.code
ORDER BY distance DESC
LIMIT 3;

-- What are the top-3 closest Intercity stations
-- using aerial distance?
SELECT
    s1.name_long AS station1,
    s2.name_long AS station2,
    ST_Distance(
        ST_Point(s1.geo_lng, s1.geo_lat),
        ST_Point(s2.geo_lng, s2.geo_lat)
    ) * 111_139 AS distance
FROM stations s1, stations s2
WHERE s1.type LIKE '%Intercity%'
  AND s2.type LIKE '%Intercity%'
  AND s1.id < s2.id
ORDER BY distance ASC
LIMIT 3;

# Get the top-3 busiest train stations
import duckdb
duckdb.sql("""
    SELECT station, count(*) AS num_services
    FROM train_services
    GROUP BY ALL
    ORDER BY num_services DESC
    LIMIT 3;
    """)

# Reading and writing Pandas dataframes
import pandas as pd
import duckdb

df_in = pd.DataFrame({
    'station': ['Delft', 'Delft', 'Gouda', 'Gouda'],
    'day': ['Mon', 'Tue', 'Mon', 'Tue'],
    'num_services' : [22, 20, 27, 25]})

# Run query on a dataframe and return a dataframe
df_out = duckdb.sql("""
    SELECT station, sum(num_services)
    FROM df_in
    GROUP BY station
    """).to_df()

# Create custom user-defined function
import duckdb

def add_plus_one(x):
    return x + 1

con = duckdb.connect()
con.create_function('add_plus_one', add_plus_one,
    ['BIGINT'], 'BIGINT', type='native')

con.sql("""
    SELECT sum(add_plus_one(i)) FROM range(10) tbl(i);
    """)

# Find the largest sepals & petals in the Iris data set
library(duckdb)

con <- dbConnect(duckdb())
duckdb_register(con, "iris", iris)

query <- r'(
SELECT count(*) AS num_observations,
max("Sepal.Width") AS max_width,
max("Petal.Length") AS max_petal_length
FROM iris
WHERE "Sepal.Length" > 5
GROUP BY ALL
)'

dbGetQuery(con, query)

# Integration with dplyr
# Find the largest sepals and petals in the Iris data set
library("duckdb")
library("dplyr")

con <- dbConnect(duckdb())
duckdb_register(con, "iris", iris)
tbl(con, "iris") |>
    filter(Sepal.Length > 5) |>
    group_by(Species) |>
    summarize(num_observations = count(),
        max_width = max(Sepal.Width),
        max_petal_length = max(Petal.Length),
        na.rm = TRUE) |>
    collect()

// Get a list of train stations by traffic
Connection conn =
    DriverManager.getConnection("jdbc:duckdb:");
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(
    "SELECT station_name, count(*) AS num_services\n" + 
    "FROM train_services\n" + 
    "GROUP BY ALL\n" + 
    "ORDER BY num_services DESC;");
    
while (rs.next()) {
    System.out.println(rs.getString(1));
    System.out.println(rs.getInt(2));
}

// Using the appender for bulk inserts
DuckDBConnection conn = (DuckDBConnection) DriverManager.getConnection("jdbc:duckdb:");
Statement stmt = conn.createStatement();
stmt.execute("CREATE TABLE person (first_name VARCHAR, last_name VARCHAR, age INT)");

try (var appender = conn.createAppender(
        DuckDBConnection.DEFAULT_SCHEMA, "tbl"
    )) {
    appender.beginRow();
    appender.append("John");
    appender.append("Smith");
    appender.append(42);
    appender.endRow();
}

// Get the top-3 busiest train stations in May
const duckdb = require('duckdb');
const db = new duckdb.Database(':memory:');
db.all(
  `SELECT station_name, count(*) AS num_services
    FROM 'http://blobs.duckdb.org/train_services.parquet'
    WHERE monthname(date) = 'May'
    GROUP BY ALL
    ORDER BY num_services DESC
    LIMIT 3;`,
  (err, res) => {
    if (err) {
      console.log("Error", err);
    } else {
      console.table(res);
    }
  }
);

// Web Service Integration:
// create endpoint to generate numbers
const express = require("express");
const duckdb = require("duckdb");
const app = express();
const db = new duckdb.Database(":memory:");
app.get("/getnumbers", (req, res) => {
  db.all("SELECT random() AS num FROM range(10)", (a, b) => {
    if (a) {
      console.warn(a);
      res.end("Error " + a);
    }
    res.end(JSON.stringify(b));
  });
});

app.listen(8082, () => console.log("Go to: http://localhost:8082/getnumbers"));