234 lines
6.9 KiB
SQL
234 lines
6.9 KiB
SQL
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-- Practical SQL: A Beginner's Guide to Storytelling with Data
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-- by Anthony DeBarros
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-- Chapter 11 Code Examples
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--------------------------------------------------------------
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-- Listing 11-1: Extracting components of a timestamp value using date_part()
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SELECT
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date_part('year', '2019-12-01 18:37:12 EST'::timestamptz) AS "year",
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date_part('month', '2019-12-01 18:37:12 EST'::timestamptz) AS "month",
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date_part('day', '2019-12-01 18:37:12 EST'::timestamptz) AS "day",
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date_part('hour', '2019-12-01 18:37:12 EST'::timestamptz) AS "hour",
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date_part('minute', '2019-12-01 18:37:12 EST'::timestamptz) AS "minute",
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date_part('seconds', '2019-12-01 18:37:12 EST'::timestamptz) AS "seconds",
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date_part('timezone_hour', '2019-12-01 18:37:12 EST'::timestamptz) AS "tz",
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date_part('week', '2019-12-01 18:37:12 EST'::timestamptz) AS "week",
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date_part('quarter', '2019-12-01 18:37:12 EST'::timestamptz) AS "quarter",
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date_part('epoch', '2019-12-01 18:37:12 EST'::timestamptz) AS "epoch";
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-- Bonus: Using the SQL-standard extract() for similar datetime parsing:
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SELECT extract('year' from '2019-12-01 18:37:12 EST'::timestamptz) AS "year";
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-- Listing 11-2: Three functions for making datetimes from components
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-- make a date
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SELECT make_date(2018, 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(2018, 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_date,
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current_time,
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current_timestamp,
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localtime,
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localtimestamp,
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now();
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-- Listing 11-3: Comparing current_timestamp and clock_timestamp() during row insert
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CREATE TABLE current_time_example (
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time_id bigserial,
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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 (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 11-4: Showing your PostgreSQL server's default time zone
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SHOW timezone; -- Note: You can see all run-time defaults with SHOW ALL;
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-- Listing 11-5: Showing time zone abbreviations and names
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SELECT * FROM pg_timezone_abbrevs;
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SELECT * FROM pg_timezone_names;
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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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-- Listing 11-6: Setting the time zone for a client session
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SET timezone TO '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 ('2020-01-01 4:00');
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SELECT test_date
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FROM time_zone_test;
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SET timezone TO '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 '9/30/1929'::date - '9/27/1929'::date;
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SELECT '9/30/1929'::date + '5 years'::interval;
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-- Taxi Rides
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-- Listing 11-7: Creating a table and importing NYC yellow taxi data
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CREATE TABLE nyc_yellow_taxi_trips_2016_06_01 (
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trip_id bigserial PRIMARY KEY,
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vendor_id varchar(1) 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 varchar(2) NOT NULL,
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store_and_fwd_flag varchar(1) 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 varchar(1) 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_2016_06_01 (
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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\yellow_tripdata_2016_06_01.csv'
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WITH (FORMAT CSV, HEADER, DELIMITER ',');
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CREATE INDEX tpep_pickup_idx
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ON nyc_yellow_taxi_trips_2016_06_01 (tpep_pickup_datetime);
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SELECT count(*) FROM nyc_yellow_taxi_trips_2016_06_01;
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-- Listing 11-8: Counting taxi trips by hour
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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_2016_06_01
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GROUP BY trip_hour
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ORDER BY trip_hour;
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-- Listing 11-9: 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_2016_06_01
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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_pickups_2016_06_01.csv'
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WITH (FORMAT CSV, HEADER, DELIMITER ',');
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-- Listing 11-10: 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_2016_06_01
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GROUP BY trip_hour
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ORDER BY trip_hour;
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-- Listing 11-11: Creating a table to hold train trip data
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SET timezone TO 'US/Central';
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CREATE TABLE train_rides (
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trip_id bigserial PRIMARY KEY,
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segment varchar(50) 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', '2017-11-13 21:30 CST', '2017-11-14 18:23 EST'),
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('New York to New Orleans', '2017-11-15 14:15 EST', '2017-11-16 19:32 CST'),
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('New Orleans to Los Angeles', '2017-11-17 13:45 CST', '2017-11-18 9:00 PST'),
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('Los Angeles to San Francisco', '2017-11-19 10:10 PST', '2017-11-19 21:24 PST'),
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('San Francisco to Denver', '2017-11-20 9:10 PST', '2017-11-21 18:38 MST'),
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('Denver to Chicago', '2017-11-22 19:10 MST', '2017-11-23 14:50 CST');
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SELECT * FROM train_rides;
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-- Listing 11-12: 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 11-13: 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 11-14: 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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