One Databyse To Rule 'em All

One Database To Rule 'em All
PHP Usergroup Berlin
November 2015
Stefanie Janine Stölting

SQL/MED
Defined by ISO/IEC 9075-9:200
Supported by
DB2
MariaDB
With CONNECT storage engine,
implementation differs to the standard
PostgreSQL

Implementation
Foreign Data Wrapper
Read only
Read and write
Installation as extensions

Available FDW
Examples:
Oracle (pgxn.org)
MS SQL Server / Sybase ASE
readonly (pgxn.org)
MongoDB
readonly (pgxn.org)
MariaDB / MySQL (github.com)

Data source
The example data used in the SQL part is
availabale from Chinook Database:
PostgreSQL
MySQL
SQLite

CTE
Common Table Expressions will be used in examples
● Example:
WITH RECURSIVE t(n) AS (
VALUES (1)
UNION ALL
SELECT n+1 FROM t WHERE n < 100
)
SELECT sum(n), min(n), max(n) FROM t;
●
Result:

Live Data examples
-- Create the foreign data wrapper extension in the current database
CREATE EXTENSION mysql_fdw;
-- Create the mapping to the foreign MariaDB server
CREATE SERVER mariadb_server
FOREIGN DATA WRAPPER mysql_fdw
OPTIONS (host '127.0.0.1', port '3306');
-- Create a user mapping with user and password of the foreign table
-- PostgreSQL gives you options to connect this user with its own users
CREATE USER MAPPING FOR PUBLIC SERVER mariadb_server
OPTIONS (username 'pg_test', password 'secret');

Live Data examples
-- Create the MariaDB foreign table, column definitions have to match
CREATE FOREIGN TABLE mysql_album(
"AlbumId" integer,
"Title" character varying(160),
"ArtistId" integer
)
SERVER mariadb_server
OPTIONS(
dbname 'Chinook',
table_name 'Album'
);
-- Select some data
SELECT * FROM mysql_album;

Live Data examples
-- Create the mapping to the foreign SQLite file
CREATE SERVER sqlite_server
FOREIGN DATA WRAPPER sqlite_fdw
OPTIONS (database '/var/sqlite/Chinook_Sqlite.sqlite')
;
-- Create the SQLite foreign table, column definitions have to match
CREATE FOREIGN TABLE sqlite_artist(
"ArtistId" integer,
"Name" character varying(120)
)
SERVER sqlite_server
OPTIONS(
table 'Artist'
);

Live Data examples
-- Select some data
SELECT * FROM sqlite_artist;

Live Data examples
-- Join PostgreSQL, MariaDB and SQLite tables
SELECT *
FROM sqlite_artist AS artist
INNER JOIN mysql_album AS album
ON artist."ArtistId" = album."ArtistId"
INNER JOIN "Track" AS track
ON album."AlbumId" = track."AlbumId"
;

Live Data examples
-- Joining SQLite and MariaDB tables using PostgreSQL expressions
WITH album AS
(
SELECT "ArtistId"
, array_agg("Title") AS album_titles
FROM mysql_album
GROUP BY "ArtistId"
)
SELECT artist."Name" AS artist
, album.album_titles
INNER JOIN album
;

Live Data examples
-- Creates an materialized view on foreign tables
CREATE MATERIALIZED VIEW mv_album_artist AS
WITH album AS
(
SELECT "ArtistId"
, array_agg("Title") AS album_titles
FROM mysql_album
GROUP BY "ArtistId"
)
SELECT artist."Name" AS artist
, SUM(ARRAY_LENGTH(album_titles, 1))
LEFT OUTER JOIN album
GROUP BY artist."Name"
;
-- Creates a unique index on a mv
CREATE UNIQUE INDEX mv_album_artist__artist ON mv_album_artist(artist);

Live Data examples
-- Select the mv data
SELECT *
FROM mv_album_artist
WHERE artist = 'AC/DC'
;

Live Data examples
-- SELECT the amount of albums from the MariaDB table from MariaDB, not with a foreign data
wrapper
SELECT count( * ) AS AlbumCount
FROM `Album`
;

Live Data examples
-- Insert data calculated from foreign tables using PostgreSQL features into another foreign table
INSERT INTO mysql_album("AlbumId", "ArtistId", "Title")
WITH album AS
(
-- Generate a new album id
SELECT MAX(album."AlbumId") + 1 AS new_album_id
FROM mysql_album AS album
)
SELECT album.new_album_id
, artist."ArtistId"
, 'Back in Black'
FROM sqlite_artist AS artist, album
WHERE artist."Name" = 'AC/DC'
GROUP BY album.new_album_id
, artist."ArtistId"
;

Live Data examples
-- Select data from the materialized view
SELECT *
FROM mv_album_artist
WHERE artist = 'AC/DC'
ORDER BY artist
;
-- Refresh the mv to see the recently added data
REFRESH MATERIALIZED VIEW mv_album_artist;
-- We can even delete data from foreign tables
DELETE FROM mysql_album
WHERE "Title" = 'Back in Black'
AND "ArtistId" = 1
;

Live Data examples
-- Using PostgreSQL JSON with data from MariaDB and SQLite
-- Step 1: Albums with tracks as JSON
WITH albums AS
(
SELECT a."ArtistId" AS artist_id
, a."Title" AS album_title
, array_agg(t."Name") AS album_tracks
FROM mysql_album AS a
INNER JOIN "Track" AS t
ON a."AlbumId" = t."AlbumId"
GROUP BY a."ArtistId"
, a."Title"
)
SELECT row_to_json(albums) AS album_tracks
FROM albums
;

Live Data examples
-- Step 2 Abums including tracks with aritsts
WITH albums AS
(
, a."Title"
)
, js_albums AS
(
FROM albums
)
SELECT a."Name" AS artist
, al.album_tracks AS albums_tracks
FROM sqlite_artist AS a
INNER JOIN js_albums AS al
ON a."ArtistId" = CAST(al.album_tracks->>'artist_id' AS INT)
;

Live Data examples
-- Step 3 Return one row for an artist with all albums
CREATE MATERIALIZED VIEW v_artist_data AS
WITH albums AS
(
, a."Title"
)
, js_albums AS
(
FROM albums
)
, artist_albums AS
(
SELECT a."Name" AS artist
, array_agg(al.album_tracks) AS albums_tracks
FROM sqlite_artist AS a
INNER JOIN js_albums AS al
ON a."ArtistId" = CAST(al.album_tracks->>'artist_id' AS INT)
GROUP BY a."Name"
)
SELECT CAST(row_to_json(artist_albums) AS JSONB) AS artist_data
FROM artist_albums
;

Live Data examples
CREATE MATERIALIZED VIEW mv_artist_data AS
SELECT *
FROM v_artist_data
;
CREATE INDEX artist_data_gin ON mv_artist_data USING
GIN(artist_data);

Live Data examples
-- SELECT data from that materialized view, that does
querying
-- PostgreSQL, MariaDB, and SQLite tables in one SQL
statement
SELECT jsonb_pretty(artist_data) pretty_artistdata
FROM mv_artist_data
WHERE artist_data->>'artist' IN ('Miles Davis', 'AC/DC')
;

Live Data examples
{
"artist": "Miles Davis",
"albums_tracks":
[
{
"artist_id": 68,
"album_title": "Miles Ahead",
"album_tracks":
[
"I Don't Wanna Be Kissed (By Anyone But You) (Alternate Take)",
"The Meaning Of The Blues/Lament (Alternate Take)",
"Blues For Pablo (Alternate Take)",
"Springsville (Alternate Take)",
...
]
},
{
...
}
]
}

Live Data examples
-- SELECT some data using JSON methods
SELECT jsonb_pretty(artist_data#>'{albums_tracks}') AS all_albums
, jsonb_pretty(artist_data#>'{albums_tracks, 0}') AS tracks_0
, artist_data#>'{albums_tracks, 0, album_title}' AS title
FROM mv_artist_data
WHERE artist_data->'albums_tracks' @> '[{"album_title":"Miles Ahead"}]'
;

User Group / Conferences
PostgreSQL User Group Berlin
German PostgreSQL Conference 2015
Hamburg, November 26-27, 2015
FOSDEM PGDay 2016
Brussels, January 29, 2016
FOSDEM 2016, PostgreSQL devroom
Brussels, January 30-31, 2016

Link List
PGXN Extensions:
- mysql_fdw, MySQL/MariaDB FDW
- sqlite_fdw, SQLite FDW
- jsonbx, PostgreSQL 9.5 JSONB features
Slide and source on Github:
https://github.com/sjstoelting/talks

One Database To Rule 'em All
This document by Stefanie Janine Stölting is covered by the
Creative Commons Attribution 4.0 International

One Databyse To Rule 'em All

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