244 lines
7.1 KiB
SQL
244 lines
7.1 KiB
SQL
---------------------------------------------------------------------------
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-- Practical SQL: A Beginner's Guide to Storytelling with Data, 2nd Edition
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-- by Anthony DeBarros
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-- Chapter 12 Code Examples
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----------------------------------------------------------------------------
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-- Listing 12-1: Extracting components of a timestamp value using date_part()
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SHOW ALL;
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SELECT
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date_part('year', '2022-12-01 18:37:12 EST'::timestamptz) AS year,
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date_part('month', '2022-12-01 18:37:12 EST'::timestamptz) AS month,
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date_part('day', '2022-12-01 18:37:12 EST'::timestamptz) AS day,
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date_part('hour', '2022-12-01 18:37:12 EST'::timestamptz) AS hour,
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date_part('minute', '2022-12-01 18:37:12 EST'::timestamptz) AS minute,
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date_part('seconds', '2022-12-01 18:37:12 EST'::timestamptz) AS seconds,
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date_part('timezone_hour', '2022-12-01 18:37:12 EST'::timestamptz) AS tz,
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date_part('week', '2022-12-01 18:37:12 EST'::timestamptz) AS week,
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date_part('quarter', '2022-12-01 18:37:12 EST'::timestamptz) AS quarter,
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date_part('epoch', '2022-12-01 18:37:12 EST'::timestamptz) AS epoch;
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SELECT '2022-12-01 18:37:12 EST'::timestamp AT TIME ZONE 'US/Pacific'
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-- Bonus: Using the SQL-standard extract() for similar datetime parsing:
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SELECT extract('year' from '2022-12-01 18:37:12 EST'::timestamptz) AS year;
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-- Listing 12-2: Three functions for making datetimes from components
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-- make a date
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SELECT make_date(2022, 2, 22);
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-- make a time
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SELECT make_time(18, 4, 30.3);
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-- make a timestamp with time zone
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SELECT make_timestamptz(2022, 2, 22, 18, 4, 30.3, 'Europe/Lisbon');
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-- Bonus: Retrieving the current date and time
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SELECT
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current_timestamp,
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localtimestamp,
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current_date,
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current_time,
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localtime,
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now();
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-- Listing 12-3: Comparing current_timestamp and clock_timestamp() during row insert
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CREATE TABLE current_time_example (
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time_id integer GENERATED ALWAYS AS IDENTITY,
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current_timestamp_col timestamp with time zone,
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clock_timestamp_col timestamp with time zone
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);
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INSERT INTO current_time_example
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(current_timestamp_col, clock_timestamp_col)
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(SELECT current_timestamp,
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clock_timestamp()
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FROM generate_series(1,1000));
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SELECT * FROM current_time_example;
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-- Time Zones
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-- Listing 12-4: Viewing your current time zone setting
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SHOW timezone; -- Note: You can see all run-time defaults with SHOW ALL;
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-- Listing 12-5: Showing time zone abbreviations and names
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SELECT * FROM pg_timezone_abbrevs ORDER BY abbrev;
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SELECT * FROM pg_timezone_names ORDER BY name;
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-- Filter to find one
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SELECT * FROM pg_timezone_names
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WHERE name LIKE 'Europe%'
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ORDER BY name;
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-- Listing 12-6: Setting the time zone for a client session
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SET TIME ZONE 'US/Pacific';
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CREATE TABLE time_zone_test (
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test_date timestamp with time zone
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);
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INSERT INTO time_zone_test VALUES ('2023-01-01 4:00');
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INSERT INTO time_zone_test VALUES ('2023-07-01 4:00');
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SELECT test_date
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FROM time_zone_test;
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SET TIME ZONE 'US/Eastern';
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SELECT test_date
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FROM time_zone_test;
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SELECT test_date AT TIME ZONE 'Asia/Seoul'
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FROM time_zone_test;
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-- Math with dates!
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SELECT '1929-09-30'::date - '1929-09-27'::date;
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SELECT '1929-09-30'::date + '5 years'::interval;
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-- Taxi Rides
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-- Listing 12-7: Creating a table and importing NYC yellow taxi data
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CREATE TABLE nyc_yellow_taxi_trips (
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trip_id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
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vendor_id text NOT NULL,
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tpep_pickup_datetime timestamp with time zone NOT NULL,
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tpep_dropoff_datetime timestamp with time zone NOT NULL,
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passenger_count integer NOT NULL,
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trip_distance numeric(8,2) NOT NULL,
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pickup_longitude numeric(18,15) NOT NULL,
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pickup_latitude numeric(18,15) NOT NULL,
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rate_code_id text NOT NULL,
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store_and_fwd_flag text NOT NULL,
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dropoff_longitude numeric(18,15) NOT NULL,
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dropoff_latitude numeric(18,15) NOT NULL,
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payment_type text NOT NULL,
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fare_amount numeric(9,2) NOT NULL,
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extra numeric(9,2) NOT NULL,
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mta_tax numeric(5,2) NOT NULL,
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tip_amount numeric(9,2) NOT NULL,
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tolls_amount numeric(9,2) NOT NULL,
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improvement_surcharge numeric(9,2) NOT NULL,
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total_amount numeric(9,2) NOT NULL
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);
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COPY nyc_yellow_taxi_trips (
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vendor_id,
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tpep_pickup_datetime,
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tpep_dropoff_datetime,
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passenger_count,
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trip_distance,
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pickup_longitude,
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pickup_latitude,
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rate_code_id,
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store_and_fwd_flag,
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dropoff_longitude,
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dropoff_latitude,
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payment_type,
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fare_amount,
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extra,
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mta_tax,
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tip_amount,
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tolls_amount,
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improvement_surcharge,
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total_amount
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)
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FROM 'C:\YourDirectory\nyc_yellow_taxi_trips.csv'
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WITH (FORMAT CSV, HEADER);
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CREATE INDEX tpep_pickup_idx
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ON nyc_yellow_taxi_trips (tpep_pickup_datetime);
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SELECT count(*) FROM nyc_yellow_taxi_trips;
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-- Listing 12-8: Counting taxi trips by hour
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SET TIME ZONE 'US/Eastern'; -- Set this if your PostgreSQL server defaults to a time zone other than US/Eastern
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SELECT
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date_part('hour', tpep_pickup_datetime) AS trip_hour,
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count(*)
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FROM nyc_yellow_taxi_trips
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GROUP BY trip_hour
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ORDER BY trip_hour;
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-- Listing 12-9: Exporting taxi pickups per hour to a CSV file
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COPY
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(SELECT
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date_part('hour', tpep_pickup_datetime) AS trip_hour,
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count(*)
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FROM nyc_yellow_taxi_trips
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GROUP BY trip_hour
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ORDER BY trip_hour
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)
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TO 'C:\YourDirectory\hourly_taxi_pickups.csv'
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WITH (FORMAT CSV, HEADER);
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-- Listing 12-10: Calculating median trip time by hour
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SELECT
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date_part('hour', tpep_pickup_datetime) AS trip_hour,
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percentile_cont(.5)
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WITHIN GROUP (ORDER BY
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tpep_dropoff_datetime - tpep_pickup_datetime) AS median_trip
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FROM nyc_yellow_taxi_trips
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GROUP BY trip_hour
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ORDER BY trip_hour;
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-- Listing 12-11: Creating a table to hold train trip data
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CREATE TABLE train_rides (
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trip_id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
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segment text NOT NULL,
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departure timestamp with time zone NOT NULL,
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arrival timestamp with time zone NOT NULL
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);
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INSERT INTO train_rides (segment, departure, arrival)
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VALUES
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('Chicago to New York', '2020-11-13 21:30 CST', '2020-11-14 18:23 EST'),
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('New York to New Orleans', '2020-11-15 14:15 EST', '2020-11-16 19:32 CST'),
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('New Orleans to Los Angeles', '2020-11-17 13:45 CST', '2020-11-18 9:00 PST'),
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('Los Angeles to San Francisco', '2020-11-19 10:10 PST', '2020-11-19 21:24 PST'),
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('San Francisco to Denver', '2020-11-20 9:10 PST', '2020-11-21 18:38 MST'),
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('Denver to Chicago', '2020-11-22 19:10 MST', '2020-11-23 14:50 CST');
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SET TIME ZONE 'US/Central';
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SELECT * FROM train_rides;
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-- Listing 12-12: Calculating the length of each trip segment
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SELECT segment,
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to_char(departure, 'YYYY-MM-DD HH12:MI a.m. TZ') AS departure,
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arrival - departure AS segment_time
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FROM train_rides;
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-- Listing 12-13: Calculating cumulative intervals using OVER
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SELECT segment,
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arrival - departure AS segment_time,
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sum(arrival - departure) OVER (ORDER BY trip_id) AS cume_time
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FROM train_rides;
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-- Listing 12-14: Better formatting for cumulative trip time
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SELECT segment,
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arrival - departure AS segment_time,
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sum(date_part('epoch', (arrival - departure)))
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OVER (ORDER BY trip_id) * interval '1 second' AS cume_time
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FROM train_rides;
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