New Chapter 16 code and data on working with JSON
This commit is contained in:
anthonydb
parent
7d9eeb5ece
commit
f9a6b17912
421
Chapter_16/Chapter_16.sql
Normal file
421
Chapter_16/Chapter_16.sql
Normal file
@ -0,0 +1,421 @@
|
|||||||
|
---------------------------------------------------------------------------
|
||||||
|
-- Practical SQL: A Beginner's Guide to Storytelling with Data, 2nd Edition
|
||||||
|
-- by Anthony DeBarros
|
||||||
|
|
||||||
|
-- Chapter 16 Code Examples
|
||||||
|
----------------------------------------------------------------------------
|
||||||
|
|
||||||
|
-- Listing 16-1: JSON with information on two films
|
||||||
|
|
||||||
|
[{
|
||||||
|
"title": "The Incredibles",
|
||||||
|
"year": 2004,
|
||||||
|
"rating": {
|
||||||
|
"MPAA": "PG"
|
||||||
|
},
|
||||||
|
"characters": [{
|
||||||
|
"name": "Mr. Incredible",
|
||||||
|
"actor": "Craig T. Nelson"
|
||||||
|
}, {
|
||||||
|
"name": "Elastigirl",
|
||||||
|
"actor": "Holly Hunter"
|
||||||
|
}, {
|
||||||
|
"name": "Frozone",
|
||||||
|
"actor": "Samuel L. Jackson"
|
||||||
|
}],
|
||||||
|
"genre": ["animation", "action", "sci-fi"]
|
||||||
|
}, {
|
||||||
|
"title": "Cinema Paradiso",
|
||||||
|
"year": 1988,
|
||||||
|
"characters": [{
|
||||||
|
"name": "Salvatore",
|
||||||
|
"actor": "Salvatore Cascio"
|
||||||
|
}, {
|
||||||
|
"name": "Alfredo",
|
||||||
|
"actor": "Philippe Noiret"
|
||||||
|
}],
|
||||||
|
"genre": ["romance", "drama"]
|
||||||
|
}]
|
||||||
|
|
||||||
|
-- Listing 16-2: Creating a table to hold JSON data and adding an index
|
||||||
|
|
||||||
|
CREATE TABLE films (
|
||||||
|
id integer GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
|
||||||
|
film jsonb
|
||||||
|
);
|
||||||
|
|
||||||
|
COPY films (film)
|
||||||
|
FROM 'C:\YourDirectory\films.json';
|
||||||
|
|
||||||
|
CREATE INDEX idx_film ON films USING GIN (film);
|
||||||
|
|
||||||
|
SELECT * FROM films;
|
||||||
|
|
||||||
|
|
||||||
|
-- JSON AND JSONB EXTRACTION OPERATORS
|
||||||
|
|
||||||
|
-- Listing 16-3: Retrieving a JSON key value with field extraction operators
|
||||||
|
|
||||||
|
-- Returns the key value as a JSON data type
|
||||||
|
SELECT id, film -> 'title' AS title
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Returns the key value as text
|
||||||
|
SELECT id, film ->> 'title' AS title
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Returns the entire array as a JSON data type
|
||||||
|
SELECT id, film -> 'genre' AS genre
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Listing 16-4: Retrieving a JSON array value with element extraction operators
|
||||||
|
|
||||||
|
-- Extracts first element of the JSON array
|
||||||
|
-- (array elements are indexed from zero, but negative integers count from the end).
|
||||||
|
SELECT id, film -> 'genre' -> 0 AS genres
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
SELECT id, film -> 'genre' -> -1 AS genres
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
SELECT id, film -> 'genre' -> 2 AS genres
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Return the array element as text
|
||||||
|
SELECT id, film -> 'genre' ->> 0 AS genres
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Listing 16-5: Retrieving a JSON key value with path extraction operators
|
||||||
|
|
||||||
|
-- Retrieve the film's MPAA rating.
|
||||||
|
SELECT id, film #> '{rating, MPAA}' AS mpaa_rating
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Retrieve the name of the first character
|
||||||
|
SELECT id, film #> '{characters, 0, name}' AS name
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Same as above but return it as text
|
||||||
|
SELECT id, film #>> '{characters, 0, name}' AS name
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
|
||||||
|
-- JSONB CONTAINMENT AND EXISTENCE OPERATORS
|
||||||
|
|
||||||
|
-- Listing 16-6: Demonstrating containment operators
|
||||||
|
|
||||||
|
-- Does the film JSON value contain the following key/value pair?
|
||||||
|
SELECT id, film ->> 'title' AS title,
|
||||||
|
film @> '{"title": "The Incredibles"}'::jsonb AS is_incredible
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Using the containment operator in WHERE
|
||||||
|
SELECT film ->> 'title' AS title,
|
||||||
|
film ->> 'year' AS year
|
||||||
|
FROM films
|
||||||
|
WHERE film @> '{"title": "The Incredibles"}'::jsonb;
|
||||||
|
|
||||||
|
-- Is the first JSON value contained in the second?
|
||||||
|
SELECT film ->> 'title' AS title,
|
||||||
|
film ->> 'year' AS year
|
||||||
|
FROM films
|
||||||
|
WHERE '{"title": "The Incredibles"}'::jsonb <@ film;
|
||||||
|
|
||||||
|
-- Listing 16-7: Demonstrating existence operators
|
||||||
|
|
||||||
|
-- Does the text string exist as a top-level key or array element within the JSON value?
|
||||||
|
SELECT film ->> 'title' AS title
|
||||||
|
FROM films
|
||||||
|
WHERE film ? 'rating';
|
||||||
|
|
||||||
|
-- Do any of the strings in the text array exist as top-level keys or array elements?
|
||||||
|
SELECT film ->> 'title' AS title,
|
||||||
|
film ->> 'rating' AS rating,
|
||||||
|
film ->> 'genre' AS genre
|
||||||
|
FROM films
|
||||||
|
WHERE film ?| '{rating, genre}';
|
||||||
|
|
||||||
|
-- Do all of the strings in the text array exist as top-level keys or array elements?
|
||||||
|
SELECT film ->> 'title' AS title,
|
||||||
|
film ->> 'rating' AS rating,
|
||||||
|
film ->> 'genre' AS genre
|
||||||
|
FROM films
|
||||||
|
WHERE film ?& '{rating, genre}';
|
||||||
|
|
||||||
|
|
||||||
|
-- ANALYZING EARTHQUAKE DATA
|
||||||
|
|
||||||
|
-- Listing 16-8: JSON with data on one earthquake
|
||||||
|
|
||||||
|
{
|
||||||
|
"type": "Feature",
|
||||||
|
"properties": {
|
||||||
|
"mag": 1.44,
|
||||||
|
"place": "134 km W of Adak, Alaska",
|
||||||
|
"time": 1612051063470,
|
||||||
|
"updated": 1612139465880,
|
||||||
|
"tz": null,
|
||||||
|
"url": "https://earthquake.usgs.gov/earthquakes/eventpage/av91018173",
|
||||||
|
"detail": "https://earthquake.usgs.gov/fdsnws/event/1/query?eventid=av91018173&format=geojson",
|
||||||
|
"felt": null,
|
||||||
|
"cdi": null,
|
||||||
|
"mmi": null,
|
||||||
|
"alert": null,
|
||||||
|
"status": "reviewed",
|
||||||
|
"tsunami": 0,
|
||||||
|
"sig": 32,
|
||||||
|
"net": "av",
|
||||||
|
"code": "91018173",
|
||||||
|
"ids": ",av91018173,",
|
||||||
|
"sources": ",av,",
|
||||||
|
"types": ",origin,phase-data,",
|
||||||
|
"nst": 10,
|
||||||
|
"dmin": null,
|
||||||
|
"rms": 0.15,
|
||||||
|
"gap": 174,
|
||||||
|
"magType": "ml",
|
||||||
|
"type": "earthquake",
|
||||||
|
"title": "M 1.4 - 134 km W of Adak, Alaska"
|
||||||
|
},
|
||||||
|
"geometry": {
|
||||||
|
"type": "Point",
|
||||||
|
"coordinates": [-178.581, 51.8418333333333, 22.48]
|
||||||
|
},
|
||||||
|
"id": "av91018173"
|
||||||
|
}
|
||||||
|
|
||||||
|
-- Listing 16-9: Creating and loading an earthquakes table
|
||||||
|
|
||||||
|
CREATE TABLE earthquakes (
|
||||||
|
id integer GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
|
||||||
|
earthquake jsonb
|
||||||
|
);
|
||||||
|
|
||||||
|
COPY earthquakes (earthquake)
|
||||||
|
FROM 'C:\YourDirectory\earthquakes.json';
|
||||||
|
|
||||||
|
CREATE INDEX idx_earthquakes ON earthquakes USING GIN (earthquake);
|
||||||
|
|
||||||
|
SELECT * FROM earthquakes;
|
||||||
|
|
||||||
|
-- Listing 16-10: Retrieving the earthquake time
|
||||||
|
-- Note that the time is stored in epoch format
|
||||||
|
|
||||||
|
SELECT id, earthquake #>> '{properties, time}' AS time
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY id LIMIT 5;
|
||||||
|
|
||||||
|
-- Listing 16-11: Converting the time value to a timestamp
|
||||||
|
|
||||||
|
SELECT id, earthquake #>> '{properties, time}' as time,
|
||||||
|
to_timestamp(
|
||||||
|
(earthquake #>> '{properties, time}')::bigint / 1000
|
||||||
|
) AS time_formatted
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY id LIMIT 5;
|
||||||
|
|
||||||
|
-- See and set time zone if desired
|
||||||
|
SHOW timezone;
|
||||||
|
SET timezone TO 'US/Eastern';
|
||||||
|
SET timezone TO 'UTC';
|
||||||
|
|
||||||
|
-- Listing 16-12: Finding the minimum and maximum earthquake times
|
||||||
|
|
||||||
|
SELECT min(to_timestamp(
|
||||||
|
(earthquake #>> '{properties, time}')::bigint / 1000
|
||||||
|
)) AT TIME ZONE 'UTC' AS min_timestamp,
|
||||||
|
max(to_timestamp(
|
||||||
|
(earthquake #>> '{properties, time}')::bigint / 1000
|
||||||
|
)) AT TIME ZONE 'UTC' AS max_timestamp
|
||||||
|
FROM earthquakes;
|
||||||
|
|
||||||
|
-- Listing 16-13: Finding the five earthquakes with the largest magnitude
|
||||||
|
|
||||||
|
SELECT earthquake #>> '{properties, place}' AS place,
|
||||||
|
to_timestamp((earthquake #>> '{properties, time}')::bigint / 1000)
|
||||||
|
AT TIME ZONE 'UTC' AS time,
|
||||||
|
(earthquake #>> '{properties, mag}')::numeric AS magnitude
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY (earthquake #>> '{properties, mag}')::numeric DESC NULLS LAST
|
||||||
|
LIMIT 5;
|
||||||
|
|
||||||
|
-- Bonus: Instead of using a path extraction operator (#>>), you can also use field extraction:
|
||||||
|
SELECT earthquake -> 'properties' ->> 'place' AS place,
|
||||||
|
to_timestamp((earthquake -> 'properties' ->> 'time')::bigint / 1000)
|
||||||
|
AT TIME ZONE 'UTC' AS time,
|
||||||
|
(earthquake #>> '{properties, mag}')::numeric AS magnitude
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY (earthquake #>> '{properties, mag}')::numeric DESC NULLS LAST
|
||||||
|
LIMIT 5;
|
||||||
|
|
||||||
|
-- Listing 16-14: Finding earthquakes with most Did You Feel It? reports
|
||||||
|
-- https://earthquake.usgs.gov/data/dyfi/
|
||||||
|
|
||||||
|
SELECT earthquake #>> '{properties, place}' AS place,
|
||||||
|
to_timestamp((earthquake #>> '{properties, time}')::bigint / 1000)
|
||||||
|
AT TIME ZONE 'UTC' AS time,
|
||||||
|
(earthquake #>> '{properties, mag}')::numeric AS magnitude,
|
||||||
|
(earthquake #>> '{properties, felt}')::integer AS felt
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY (earthquake #>> '{properties, felt}')::integer DESC NULLS LAST
|
||||||
|
LIMIT 5;
|
||||||
|
|
||||||
|
-- Listing 16-15: Extracting the earthquake's location data
|
||||||
|
|
||||||
|
SELECT id,
|
||||||
|
earthquake #>> '{geometry, coordinates}' AS coordinates,
|
||||||
|
earthquake #>> '{geometry, coordinates, 0}' AS longitude,
|
||||||
|
earthquake #>> '{geometry, coordinates, 1}' AS latitude
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY id
|
||||||
|
LIMIT 5;
|
||||||
|
|
||||||
|
-- Listing 16-16: Converting JSON location data to PostGIS geography
|
||||||
|
SELECT ST_SetSRID(
|
||||||
|
ST_MakePoint(
|
||||||
|
(earthquake #>> '{geometry, coordinates, 0}')::numeric,
|
||||||
|
(earthquake #>> '{geometry, coordinates, 1}')::numeric
|
||||||
|
),
|
||||||
|
4326)::geography AS earthquake_point
|
||||||
|
FROM earthquakes
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Listing 16-17: Finding earthquakes within 50 miles of downtown Tulsa, Oklahoma
|
||||||
|
|
||||||
|
-- Add a column of the geography data type
|
||||||
|
ALTER TABLE earthquakes ADD COLUMN earthquake_point geography(POINT, 4326);
|
||||||
|
|
||||||
|
-- Update the earthquakes table with a Point
|
||||||
|
UPDATE earthquakes
|
||||||
|
SET earthquake_point =
|
||||||
|
ST_SetSRID(
|
||||||
|
ST_MakePoint(
|
||||||
|
(earthquake #>> '{geometry, coordinates, 0}')::numeric,
|
||||||
|
(earthquake #>> '{geometry, coordinates, 1}')::numeric
|
||||||
|
),
|
||||||
|
4326)::geography;
|
||||||
|
|
||||||
|
CREATE INDEX quake_pt_idx ON earthquakes USING GIST (earthquake_point);
|
||||||
|
|
||||||
|
-- Earthquakes 50 miles from Tulsa
|
||||||
|
SELECT earthquake #>> '{properties, place}' AS place,
|
||||||
|
to_timestamp((earthquake -> 'properties' ->> 'time')::bigint / 1000)
|
||||||
|
AT TIME ZONE 'UTC' AS time,
|
||||||
|
(earthquake #>> '{properties, mag}')::numeric AS magnitude,
|
||||||
|
earthquake_point
|
||||||
|
FROM earthquakes
|
||||||
|
WHERE ST_DWithin(earthquake_point,
|
||||||
|
ST_GeogFromText('POINT(-95.989505 36.155007)'),
|
||||||
|
80468)
|
||||||
|
ORDER BY time;
|
||||||
|
|
||||||
|
-- GENERATING AND MANIPULATING JSON
|
||||||
|
|
||||||
|
-- Listing 16-18: Turning query results into JSON with row_to_json() and json_agg()
|
||||||
|
|
||||||
|
-- Convert an entire row from the table
|
||||||
|
SELECT to_json(employees) AS json_rows
|
||||||
|
FROM employees;
|
||||||
|
|
||||||
|
-- Selected columns from the table (returns key names as f1, f2, etc.)
|
||||||
|
SELECT to_json(row(emp_id, last_name)) AS json_rows
|
||||||
|
FROM employees;
|
||||||
|
|
||||||
|
-- Generating key names with a subquery
|
||||||
|
SELECT to_json(employees) AS json_rows
|
||||||
|
FROM (
|
||||||
|
SELECT emp_id, last_name AS ln FROM employees
|
||||||
|
) AS employees;
|
||||||
|
|
||||||
|
-- Aggregating the rows and converting to JSON
|
||||||
|
SELECT json_agg(to_json(employees)) AS json
|
||||||
|
FROM (
|
||||||
|
SELECT emp_id, last_name AS ln FROM employees
|
||||||
|
) AS employees;
|
||||||
|
|
||||||
|
-- Listing 16-19: Adding a top-level key/value pair via concatenation
|
||||||
|
-- Two examples
|
||||||
|
|
||||||
|
UPDATE films
|
||||||
|
SET film = film || '{"studio": "Pixar"}'::jsonb
|
||||||
|
WHERE film @> '{"title": "The Incredibles"}'::jsonb;
|
||||||
|
|
||||||
|
UPDATE films
|
||||||
|
SET film = film || jsonb_build_object('studio', 'Pixar')
|
||||||
|
WHERE film @> '{"title": "The Incredibles"}'::jsonb;
|
||||||
|
|
||||||
|
SELECT film FROM films -- check the updated data
|
||||||
|
WHERE film @> '{"title": "The Incredibles"}'::jsonb;
|
||||||
|
|
||||||
|
-- Listing 16-20: Setting an array value at a path
|
||||||
|
|
||||||
|
UPDATE films
|
||||||
|
SET film = jsonb_set(film,
|
||||||
|
'{genre}',
|
||||||
|
film #> '{genre}' || '["World War II"]',
|
||||||
|
false)
|
||||||
|
WHERE film @> '{"title": "Cinema Paradiso"}'::jsonb;
|
||||||
|
|
||||||
|
SELECT film FROM films -- check the updated data
|
||||||
|
WHERE film @> '{"title": "Cinema Paradiso"}'::jsonb;
|
||||||
|
|
||||||
|
|
||||||
|
-- Listing 16-21: Deleting values from JSON
|
||||||
|
|
||||||
|
-- Removes the studio key/value pair from The Incredibles
|
||||||
|
UPDATE films
|
||||||
|
SET film = film - 'studio'
|
||||||
|
WHERE film @> '{"title": "The Incredibles"}'::jsonb;
|
||||||
|
|
||||||
|
-- Removes the third element in the genre array of Cinema Paradiso
|
||||||
|
UPDATE films
|
||||||
|
SET film = film #- '{genre, 2}'
|
||||||
|
WHERE film @> '{"title": "Cinema Paradiso"}'::jsonb;
|
||||||
|
|
||||||
|
|
||||||
|
-- JSON PROCESSING FUNCTIONS
|
||||||
|
|
||||||
|
-- Listing 16-22: Finding the length of an array
|
||||||
|
|
||||||
|
SELECT id,
|
||||||
|
film ->> 'title' AS title,
|
||||||
|
jsonb_array_length(film -> 'characters') AS num_characters
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Listing 16-23: Returning array elements as rows
|
||||||
|
|
||||||
|
SELECT id,
|
||||||
|
jsonb_array_elements(film -> 'genre') AS genre_jsonb,
|
||||||
|
jsonb_array_elements_text(film -> 'genre') AS genre_text
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
-- Listing 16-24: Returning key values from each item in an array
|
||||||
|
|
||||||
|
SELECT id,
|
||||||
|
jsonb_array_elements(film -> 'characters')
|
||||||
|
FROM films
|
||||||
|
ORDER BY id;
|
||||||
|
|
||||||
|
WITH characters (id, json) AS (
|
||||||
|
SELECT id,
|
||||||
|
jsonb_array_elements(film -> 'characters')
|
||||||
|
FROM films
|
||||||
|
)
|
||||||
|
SELECT id,
|
||||||
|
json ->> 'name' AS name,
|
||||||
|
json ->> 'actor' AS actor
|
||||||
|
FROM characters
|
||||||
|
ORDER BY id;
|
||||||
12899
Chapter_16/earthquakes.json
Normal file
12899
Chapter_16/earthquakes.json
Normal file
File diff suppressed because it is too large
Load Diff
2
Chapter_16/films.json
Normal file
2
Chapter_16/films.json
Normal file
@ -0,0 +1,2 @@
|
|||||||
|
{"title": "The Incredibles", "year": 2004, "rating": {"MPAA": "PG"}, "characters": [{"name": "Mr. Incredible", "actor": "Craig T. Nelson"}, {"name": "Elastigirl", "actor": "Holly Hunter"}, {"name": "Frozone", "actor": "Samuel L. Jackson"}], "genre": ["animation", "action", "sci-fi"]}
|
||||||
|
{"title": "Cinema Paradiso", "year": 1988, "characters": [{"name": "Salvatore", "actor": "Salvatore Cascio"}, {"name": "Alfredo", "actor": "Philippe Noiret"}], "genre": ["romance", "drama"]}
|
||||||
@ -1012,3 +1012,128 @@ ORDER BY census.statefp, census.name;
|
|||||||
-- Note that this query also highlights a farmer's market that is mis-geocoded.
|
-- Note that this query also highlights a farmer's market that is mis-geocoded.
|
||||||
-- Can you spot it?
|
-- Can you spot it?
|
||||||
|
|
||||||
|
----------------------------------------------------------------------------
|
||||||
|
-- Chapter 16: Working with JSON Data
|
||||||
|
----------------------------------------------------------------------------
|
||||||
|
|
||||||
|
-- 1. The earthquakes JSON has a key tsunami that’s set to a value of 1 for
|
||||||
|
-- large earthquakes in oceanic regions (though it doesn’t mean a tsunami
|
||||||
|
-- actually happened). Using either path or element extraction operators,
|
||||||
|
-- find earthquakes with a tsunami value of 1 and include their location, time
|
||||||
|
-- and magnitude in your results.
|
||||||
|
|
||||||
|
-- Answer:
|
||||||
|
|
||||||
|
SELECT earthquake -> 'properties' ->> 'place' AS place,
|
||||||
|
to_timestamp((earthquake -> 'properties' ->> 'time')::bigint / 1000) AS timestamp,
|
||||||
|
(earthquake -> 'properties' ->> 'mag')::numeric AS mag
|
||||||
|
FROM earthquakes
|
||||||
|
WHERE (earthquake -> 'properties' ->> 'tsunami') = '1';
|
||||||
|
|
||||||
|
-- Same result but using path extraction operators instead of field extraction operators
|
||||||
|
SELECT earthquake #>> '{properties, place}' AS place,
|
||||||
|
to_timestamp((earthquake -> 'properties' ->> 'time')::bigint / 1000) AS timestamp,
|
||||||
|
(earthquake #>> '{properties, mag}')::numeric AS mag
|
||||||
|
FROM earthquakes
|
||||||
|
WHERE (earthquake #>> '{properties, tsunami}') = '1';
|
||||||
|
|
||||||
|
-- 2. Use the following CREATE TABLE statement to add the table earthquakes_from_json
|
||||||
|
-- to your analysis database:
|
||||||
|
|
||||||
|
CREATE TABLE earthquakes_from_json (
|
||||||
|
id text PRIMARY KEY,
|
||||||
|
title text,
|
||||||
|
type text,
|
||||||
|
quake_date timestamp with time zone,
|
||||||
|
mag numeric,
|
||||||
|
place text,
|
||||||
|
earthquake_point geography(POINT, 4326),
|
||||||
|
url text
|
||||||
|
);
|
||||||
|
|
||||||
|
-- Using field and path extraction operators, write an INSERT statement
|
||||||
|
-- to fill the table with the correct values for each earthquake. Refer
|
||||||
|
-- to the full sample earthquake JSON in your Chapter_16.sql file for any
|
||||||
|
-- key names and paths you need.
|
||||||
|
|
||||||
|
-- Answer:
|
||||||
|
-- Note that you could use either field or path operators to retrieve the needed elements.
|
||||||
|
|
||||||
|
INSERT INTO earthquakes_from_json
|
||||||
|
SELECT earthquake ->> 'id',
|
||||||
|
earthquake -> 'properties' ->> 'title',
|
||||||
|
earthquake -> 'properties' ->> 'type',
|
||||||
|
to_timestamp((earthquake -> 'properties' ->> 'time')::bigint / 1000),
|
||||||
|
(earthquake -> 'properties' ->> 'mag')::numeric,
|
||||||
|
earthquake -> 'properties' ->> 'place',
|
||||||
|
ST_SetSRID(
|
||||||
|
ST_MakePoint(
|
||||||
|
(earthquake #>> '{geometry, coordinates, 0}')::numeric,
|
||||||
|
(earthquake #>> '{geometry, coordinates, 1}')::numeric
|
||||||
|
),
|
||||||
|
4326)::geography,
|
||||||
|
earthquake -> 'properties' ->> 'url'
|
||||||
|
FROM earthquakes;
|
||||||
|
|
||||||
|
-- View the copied data:
|
||||||
|
SELECT * FROM earthquakes_from_json;
|
||||||
|
|
||||||
|
|
||||||
|
-- 3. Bonus (difficult) question: Try writing a query to generate the
|
||||||
|
-- following JSON using the data in the teachers and teachers_lab_access
|
||||||
|
-- tables from Chapter 13:
|
||||||
|
{
|
||||||
|
"id": 6,
|
||||||
|
"fn": "Kathleen",
|
||||||
|
"ln": "Roush",
|
||||||
|
"lab_access": [{
|
||||||
|
"lab_name": "Science B",
|
||||||
|
"access_time": "2022-12-17T16:00:00-05:00"
|
||||||
|
}, {
|
||||||
|
"lab_name": "Science A",
|
||||||
|
"access_time": "2022-12-07T10:02:00-05:00"
|
||||||
|
}]
|
||||||
|
}
|
||||||
|
-- It’s helpful to remember that the teachers table has a one-to-many relationship
|
||||||
|
-- with teachers_lab_access; the first three keys must come from teachers, and the
|
||||||
|
-- JSON objects in the array of lab_access will come from teachers_lab_access.
|
||||||
|
-- Hint: you’ll need to use a subquery in your SELECT list and a function called
|
||||||
|
-- json_agg() to create the lab_access array.
|
||||||
|
|
||||||
|
-- Answer:
|
||||||
|
|
||||||
|
SELECT to_json(teachers_labs)
|
||||||
|
FROM (
|
||||||
|
SELECT id,
|
||||||
|
first_name AS fn,
|
||||||
|
last_name AS ln,
|
||||||
|
(
|
||||||
|
SELECT json_agg(to_json(la))
|
||||||
|
FROM (
|
||||||
|
SELECT lab_name, access_time
|
||||||
|
FROM teachers_lab_access
|
||||||
|
WHERE teacher_id = teachers.id
|
||||||
|
ORDER BY access_time DESC
|
||||||
|
) AS la
|
||||||
|
) AS lab_access
|
||||||
|
FROM teachers
|
||||||
|
WHERE id = 6)
|
||||||
|
AS teachers_labs;
|
||||||
|
|
||||||
|
-- What's happening here? Structurally, we have a series of nested subqueries.
|
||||||
|
-- We use the first subquery to retrieve the id, first_name, and last_name columns from
|
||||||
|
-- the teachers table. In that subquery's SELECT list, we place another subquery that
|
||||||
|
-- retrieves the lab_name and access_time from the teachers_lab_access.
|
||||||
|
|
||||||
|
-- What makes this query tricky is that we need to use an inner subquery to generate the
|
||||||
|
-- lab access objects and use the json_agg function to aggregate the results of those rows
|
||||||
|
-- into an array.
|
||||||
|
|
||||||
|
-- When writing a query such as this, it's helpful to work in chunks. Start with the
|
||||||
|
-- outermost query and add the subqueries one by one, testing as you go.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|||||||
Loading…
x
Reference in New Issue
Block a user