Intro to Cypher for the SQL Developer

Cypher for SQL Developers
Mark Needham
@markhneedham
mark@neo4j.com

Talk structure
‣ Introduce data set
‣ Modeling
‣ Import
‣ Data Integrity
‣ Queries
‣ Migration/Refactoring
‣ Query optimisation

Exploring transfermarkt
|---------+--------------------+-----------------------------------------+--------------------+------------|
| season | playerName | playerUri | playerPosition | playerAge |
|---------+--------------------+-----------------------------------------+--------------------+------------|
| 90/91 | Aldair | /aldair/profil/spieler/4151 | Centre Back | 24 |
| 90/91 | Thomas Häßler | /thomas-hassler/profil/spieler/553 | Attacking Midfield | 24 |
| 90/91 | Roberto Baggio | /roberto-baggio/profil/spieler/4153 | Secondary Striker | 23 |
| 90/91 | Karl-Heinz Riedle | /karl-heinz-riedle/profil/spieler/13806 | Centre Forward | 24 |
| 90/91 | Henrik Larsen | /henrik-larsen/profil/spieler/101330 | Attacking Midfield | 24 |
| 90/91 | Gheorghe Hagi | /gheorghe-hagi/profil/spieler/7939 | Attacking Midfield | 25 |
| 90/91 | Hristo Stoichkov | /hristo-stoichkov/profil/spieler/7938 | Left Wing | 24 |
| 90/91 | Brian Laudrup | /brian-laudrup/profil/spieler/39667 | Centre Forward | 21 |
| 90/91 | Miguel Ángel Nadal | /miguel-angel-nadal/profil/spieler/7676 | Centre Back | 23 |
|---------+--------------------+-----------------------------------------+--------------------+------------|

|-------------------+---------------------+-------------------------------------+--------------------|
| sellerClubName | sellerClubNameShort | sellerClubUri | sellerClubCountry |
|-------------------+---------------------+-------------------------------------+--------------------|
| SL Benfica | Benfica | /benfica/startseite/verein/294 | Portugal |
| 1. FC Köln | 1. FC Köln | /1-fc-koln/startseite/verein/3 | Germany |
| ACF Fiorentina | Fiorentina | /fiorentina/startseite/verein/430 | Italy |
| SV Werder Bremen | Werder Bremen | /werder-bremen/startseite/verein/86 | Germany |
| Lyngby BK | Lyngby BK | /lyngby-bk/startseite/verein/369 | Denmark |
| Steaua Bucharest | Steaua | /steaua/startseite/verein/301 | Romania |
| CSKA Sofia | CSKA Sofia | /cska-sofia/startseite/verein/208 | Bulgaria |
| KFC Uerdingen 05 | KFC Uerdingen | /kfc-uerdingen/startseite/verein/95 | Germany |
| RCD Mallorca | RCD Mallorca | /rcd-mallorca/startseite/verein/237 | Spain |
|-------------------+---------------------+-------------------------------------+--------------------|

|----------------+--------------------+-------------------------------------+-------------------|
| buyerClubName | buyerClubNameShort | buyerClubUri | buyerClubCountry |
|----------------+--------------------+-------------------------------------+-------------------|
| AS Roma | AS Roma | /as-roma/startseite/verein/12 | Italy |
| Juventus FC | Juventus | /juventus/startseite/verein/506 | Italy |
| Juventus FC | Juventus | /juventus/startseite/verein/506 | Italy |
| SS Lazio | Lazio | /lazio/startseite/verein/398 | Italy |
| AC Pisa 1909 | AC Pisa | /ac-pisa/startseite/verein/4172 | Italy |
| Real Madrid | Real Madrid | /real-madrid/startseite/verein/418 | Spain |
| FC Barcelona | FC Barcelona | /fc-barcelona/startseite/verein/131 | Spain |
| Bayern Munich | Bayern Munich | /bayern-munich/startseite/verein/27 | Germany |
| FC Barcelona | FC Barcelona | /fc-barcelona/startseite/verein/131 | Spain |
|----------------+--------------------+-------------------------------------+-------------------|

|--------------------------------------------------------+-------------+---------------|
| transferUri | transferFee | transferRank |
|--------------------------------------------------------+-------------+---------------|
| /jumplist/transfers/spieler/4151/transfer_id/6993 | £6.75m | 1 |
|--------------------------------------------------------+-------------+---------------|

Relational Model
players
id
name
position
clubs
id
name
country
transfers
id
fee
player_age
player_id
from_club_id
to_club_id
season

Relational vs Graph
Records
in tables
Nodes
"Soft"
relationships
computed at
query time
"Hard"
relationships
built into the
data store

Create players table
CREATE TABLE players (
"id" character varying(100)
NOT NULL PRIMARY KEY,
"name" character varying(150) NOT NULL,
"position" character varying(20)
);

Insert players
INSERT INTO players
VALUES('/aldair/profil/spieler/4151', 'Aldair', 'Centre Back');
INSERT INTO players
VALUES('/thomas-hassler/profil/spieler/553', 'Thomas Häßler',
'Attacking Midfield');
INSERT INTO players VALUES('/roberto-
baggio/profil/spieler/4153', 'Roberto Baggio', 'Secondary
Striker');

Create clubs table
CREATE TABLE clubs (
"country" character varying(50)
);

Insert clubs
INSERT INTO clubs VALUES('/hertha-bsc/startseite/verein/44',
'Hertha BSC', 'Germany');
INSERT INTO clubs VALUES('/cfr-cluj/startseite/verein/7769',
'CFR Cluj', 'Romania');
INSERT INTO clubs VALUES('/real-sociedad/startseite/verein/681',
'Real Sociedad', 'Spain');

Create transfers table
CREATE TABLE transfers (
"id" character varying(100) NOT NULL PRIMARY KEY,
"fee" character varying(50) NOT NULL,
"numericFee" integer NOT NULL,
"player_age" smallint NOT NULL,
"season" character varying(5) NOT NULL,
"player_id" character varying(100) NOT NULL REFERENCES players (id),
"from_club_id" character varying(100) NOT NULL REFERENCES clubs (id),
"to_club_id" character varying(100) NOT NULL REFERENCES clubs (id)
);

Insert transfers
INSERT INTO transfers VALUES('/jumplist/transfers/spieler/4151/transfer_id/6993',
'£6.75m', 6750000, '90/91', 24, '/aldair/profil/spieler/4151',
'/benfica/startseite/verein/294', '/as-roma/startseite/verein/12');
'£5.85m', 5850000, '90/91', 24, '/thomas-hassler/profil/spieler/553', '/1-fc-
koln/startseite/verein/3', '/juventus/startseite/verein/506');
'£5.81m', 5810000, '90/91', 23, '/roberto-baggio/profil/spieler/4153',
'/fiorentina/startseite/verein/430', '/juventus/startseite/verein/506');

LOAD CSV
‣ Tool for importing CSV files
‣ Intended for data sets of ~10M records
‣ Works against live database
‣ Use Cypher constructs to define graph

LOAD CSV
[USING PERIODIC COMMIT [1000]]
LOAD CSV WITH HEADERS FROM "(file|http)://" AS row
MATCH (:Label {property: row.header})
CREATE (:Label {property: row.header})
MERGE (:Label {property: row.header})

Exploring the data
LOAD CSV WITH HEADERS
FROM "file:///transfers.csv"
AS row
RETURN COUNT(*)

Exploring the data
FROM "file:///transfers.csv"
AS row
RETURN row
LIMIT 1

Import players
USING PERIODIC COMMIT
LOAD CSV WITH HEADERS FROM "file:///transfers.csv" AS row
CREATE (player:Player {
id: row.playerUri,
name: row.playerName,
position: row.playerPosition
})

Import players
id: row.playerUri,
})
Not so fast!

Ensure uniqueness of players
CREATE CONSTRAINT ON (player:Player)
ASSERT player.id IS UNIQUE

Import players
id: row.playerUri,
})
Node 25 already exists with label Player and property "id"=[/peter-
lux/profil/spieler/84682]

Import players
MERGE (player:Player {id: row.playerUri})
ON CREATE SET player.name = row.playerName,
player.position = row.playerPosition

Import clubs
CREATE CONSTRAINT ON (club:Club)
ASSERT club.id IS UNIQUE

Import selling clubs
MERGE (club:Club {id: row.sellerClubUri})
ON CREATE SET club.name = row.sellerClubName,
club.country = row.sellerClubCountry

Import buying clubs
MERGE (club:Club {id: row.buyerClubUri})
ON CREATE SET club.name = row.buyerClubName,
club.country = row.buyerClubCountry

Import transfers
CREATE CONSTRAINT ON (transfer:Transfer)
ASSERT transfer.id IS UNIQUE

Import transfers
MATCH (player:Player {id: row.playerUri})
MATCH (source:Club {id: row.sellerClubUri})
MATCH (destination:Club {id: row.buyerClubUri})
MERGE (t:Transfer {id: row.transferUri})
ON CREATE SET t.season = row.season, t.rank = row.transferRank,
t.fee = row.transferFee
MERGE (t)-[:OF_PLAYER { age: row.playerAge }]->(player)
MERGE (t)-[:FROM_CLUB]->(source)
MERGE (t)-[:TO_CLUB]->(destination)

Optional Schema
‣ Unique node property constraint

Optional Schema
ASSERT club.id IS UNIQUE

Optional Schema
‣ Node property existence constraint

Optional Schema
ASSERT EXISTS(club.name)

Optional Schema
‣ Relationship property existence constraint

Optional Schema
‣ Relationship property existence constraint
CREATE CONSTRAINT ON ()-[player:OF_PLAYER]-()
ASSERT exists(player.age)

SELECT *
FROM players
WHERE players.name = 'Cristiano Ronaldo'

SELECT *
FROM players
WHERE players.name = 'Cristiano Ronaldo'
MATCH (player:Player { name: "Cristiano Ronaldo" })
RETURN player

SELECT players.name, t."numericFee", t.season
FROM transfers AS t
JOIN clubs AS clubFrom ON t.from_club_id = clubFrom.id
JOIN clubs AS clubTo ON t.to_club_id = clubTo.id
JOIN players ON t.player_id = players.id
WHERE clubFrom.name = 'Tottenham Hotspur'
AND clubTo.name = 'Manchester United'

SELECT players.name, t."numericFee", t.season
FROM transfers AS t
WHERE clubFrom.name = 'Tottenham Hotspur'
AND clubTo.name = 'Manchester United'
MATCH (from:Club)<-[:FROM_CLUB]-(transfer:Transfer)-[:TO_CLUB]->(to:Club),
(transfer)-[:OF_PLAYER]->(player)
WHERE from.name = "Tottenham Hotspur" AND to.name = "Manchester United"
RETURN player.name, transfer.numericFee, transfer.season

How does Neo4j use indexes?
Indexes are only used to find the starting
point for queries.
Use index scans to look up
rows in tables and join them
with rows from other tables
Use indexes to find the starting
points for a query.
Relational
Graph

Migrating/refactoring
the model

Player nationality
|------------------------------------------+--------------------+--------------------|
| playerUri | playerName | playerNationality |
|------------------------------------------+--------------------+--------------------|
| /aldair/profil/spieler/4151 | Aldair | Brazil |
| /thomas-hassler/profil/spieler/553 | Thomas Häßler | Germany |
| /roberto-baggio/profil/spieler/4153 | Roberto Baggio | Italy |
| /karl-heinz-riedle/profil/spieler/13806 | Karl-Heinz Riedle | Germany |
| /henrik-larsen/profil/spieler/101330 | Henrik Larsen | Denmark |
| /gheorghe-hagi/profil/spieler/7939 | Gheorghe Hagi | Romania |
| /hristo-stoichkov/profil/spieler/7938 | Hristo Stoichkov | Bulgaria |
| /brian-laudrup/profil/spieler/39667 | Brian Laudrup | Denmark |
| /miguel-angel-nadal/profil/spieler/7676 | Miguel Ángel Nadal | Spain |
|------------------------------------------+--------------------+--------------------|

Relational Model
players
id
name
position
nationality
clubs
id
name
country
transfers
id
fee
player_age
player_id
from_club_id
to_club_id
season

Add column to players table
ALTER TABLE players
ADD COLUMN nationality varying(30);

Update players table
UPDATE players
SET nationality = 'Brazil'
WHERE players.id = '/aldair/profil/spieler/4151';
UPDATE players
SET nationality = 'Germany'
WHERE players.id ='/ulf-kirsten/profil/spieler/74';
UPDATE players
SET nationality = 'England'
WHERE players.id ='/john-lukic/profil/spieler/28241';

Add property to player nodes
MATCH (player:Player {id: row.playerUri})
SET player.nationality = row.playerNationality

Find transfers of English
players

SELECT players.name, clubFrom.name, clubTo.name, t."numericFee", t.season
FROM transfers AS t
WHERE clubFrom.country = 'England' AND clubTo.country = 'England'
AND players.nationality = 'England'
ORDER BY t."numericFee" DESC
LIMIT 10

FROM transfers AS t
WHERE clubFrom.country = 'England' AND clubTo.country = 'England'
AND players.nationality = 'England'
LIMIT 10
MATCH (to:Club)<-[:TO_CLUB]-(t:Transfer)-[:FROM_CLUB]-(from:Club),
(t)-[:OF_PLAYER]->(player:Player)
WHERE to.country = "England" AND from.country = "England"
AND player.nationality = "England"
RETURN player.name, from.name, to.name, t.numericFee, t.season
ORDER BY t.numericFee DESC
LIMIT 10

Countries and confederations
|----------------------+----------------|
| country | confederation |
|----------------------+----------------|
| Afghanistan | afc |
| Albania | uefa |
| Algeria | caf |
| American Samoa | ofc |
| Andorra | uefa |
| Angola | caf |
| Anguilla | concacaf |
| Antigua and Barbuda | concacaf |
| Argentina | conmebol |
|----------------------+----------------|
|-----------+-----------+-------------------------------------------------|
| urlName | shortName | region |
|-----------+-----------+-------------------------------------------------|
| afc | AFC | Asia |
| uefa | UEFA | Europe |
| ofc | OFC | Oceania |
| conmebol | CONMEBOL | South America |
| concacaf | CONCACAF | North American, Central American and Caribbean |
| caf | CAF | Africa |
|-----------+-----------+-------------------------------------------------|

Relational Model
players
id
name
position
country_id
clubs
id
name
country_id
transfers
id
fee
player_age
player_id
from_club_id
to_club_id
season
countries
id
name
confederation_id
confederations
id
shortName
name
region

Create confederations table
CREATE TABLE confederations (
"shortName" character varying(50) NOT NULL,
"region" character varying(100) NOT NULL
);

Populate confederations
INSERT INTO confederations VALUES('afc', 'AFC', 'Asian Football
Confederation', 'Asia');
INSERT INTO confederations VALUES('uefa', 'UEFA', 'Union of European
Football Associations', 'Europe');
INSERT INTO confederations VALUES('ofc', 'OFC', 'Oceania Football
Confederation', 'Oceania');

Create countries table
CREATE TABLE countries (
"code" character varying(3)
"name" character varying(50)
NOT NULL,
"federation" character varying(10) NOT NULL
REFERENCES confederations (id)
);

Populate countries
INSERT INTO countries VALUES('MNE', 'Montenegro', 'uefa');
INSERT INTO countries VALUES('LTU', 'Lithuania', 'uefa');
INSERT INTO countries VALUES('CAM', 'Cambodia', 'afc');
INSERT INTO countries VALUES('SUI', 'Switzerland', 'uefa');
INSERT INTO countries VALUES('ETH', 'Ethiopia', 'caf');
INSERT INTO countries VALUES('ARU', 'Aruba', 'concacaf');
INSERT INTO countries VALUES('SWZ', 'Swaziland', 'caf');
INSERT INTO countries VALUES('PLE', 'Palestine', 'afc');

Add column to clubs table
ALTER TABLE clubs
ADD COLUMN country_id character varying(3)
REFERENCES countries(code);

Update clubs
UPDATE clubs AS cl
SET country_id = c.code
FROM clubs
INNER JOIN countries AS c
ON c.name = clubs.country
WHERE cl.id = clubs.id;

Remove country
ALTER TABLE clubs
DROP COLUMN country;

Add column to players table
ALTER TABLE players
ADD COLUMN country_id character varying(3)
REFERENCES countries(code);

Update players
UPDATE players AS p
SET country_id = c.code
FROM players
INNER JOIN countries AS c
ON c.name = players.nationality
WHERE p.id = players.id;

Remove nationality
ALTER TABLE players
DROP COLUMN nationality;

Import confederations
FROM "file:///confederations.csv" AS row
MERGE (c:Confederation {id: row.urlName})
ON CREATE
SET c.shortName = row.shortName,
c.region = row.region,
c.name = row.name

Import countries
LOAD CSV WITH HEADERS FROM "file:///countries.csv"
AS row
MERGE (country:Country {id: row.countryCode})
ON CREATE SET country.name = row.country
WITH country, row
MATCH (conf:Confederation {id: row.confederation })
MERGE (country)-[:PART_OF]->(conf)

Refactor clubs
MATCH (club:Club)
MATCH (country:Country {name: club.country})
MERGE (club)-[:PART_OF]->(country)
REMOVE club.country

Refactor players
MATCH (player:Player)
MATCH (country:Country {name: player.nationality})
MERGE (player)-[:PLAYS_FOR]->(country)
REMOVE player.nationality

Recap: Find transfers of
English players

FROM transfers AS t
JOIN countries AS fromCount ON clubFrom.country_id = fromCount.code
JOIN countries AS toCount ON clubTo.country_id = toCount.code
JOIN countries AS playerCount ON players.country_id = playerCount.code
WHERE fromCount.name = 'England' AND toCount.name = 'England' AND playerCount.name = 'England'
LIMIT 10
(t)-[:OF_PLAYER]->(player:Player)-[:PLAYS_FOR]->(country:Country),
(to)-[:PART_OF]->(country)<-[:PART_OF]-(from)
WHERE country.name = "England"
LIMIT 10

Find transfers between
different confederations

SELECT * FROM transfers AS t
JOIN countries AS fromCountry ON clubFrom.country_id = fromCountry.code
JOIN countries AS toCountry ON clubTo.country_id = toCountry.code
JOIN confederations AS fromConfederation ON fromCountry.federation = fromConfederation.id
JOIN confederations AS toConfederation ON toCountry.federation = toConfederation.id
WHERE fromConfederation.id = 'afc' AND toConfederation.id = 'uefa'
LIMIT 10

SELECT * FROM transfers AS t
JOIN countries AS fromCountry ON clubFrom.country_id = fromCountry.code
JOIN countries AS toCountry ON clubTo.country_id = toCountry.code
JOIN confederations AS fromConfederation ON fromCountry.federation = fromConfederation.id
JOIN confederations AS toConfederation ON toCountry.federation = toConfederation.id
WHERE fromConfederation.id = 'afc' AND toConfederation.id = 'uefa'
LIMIT 10
(t)-[:OF_PLAYER]->(player:Player),
(from)-[:PART_OF*2]->(:Confederation {id: "afc"}),
(to)-[:PART_OF*2]->(:Confederation {id: "uefa"})
LIMIT 10

:schema
Indexes
ON :Club(name) ONLINE
ON :Club(id) ONLINE (for uniqueness constraint)
ON :Player(name) ONLINE
ON :Player(id) ONLINE (for uniqueness constraint)
Constraints
ON (player:Player) ASSERT player.id IS UNIQUE
ON (club:Club) ASSERT exists(club.name)
ON (club:Club) ASSERT club.id IS UNIQUE
ON ()-[of_player:OF_PLAYER]-() ASSERT exists(of_player.age)
Graph schema

Graph schema
MATCH (club:Club)
RETURN keys(club), COUNT(*) AS times
+---------------------------------+
| keys(club) | times |
+---------------------------------+
| ["id","name"] | 806 |
| ["name","country","id"] | 1 |
+---------------------------------+

Meta graph
MATCH (a)-[r]->(b)
WITH head(labels(a)) AS l,
head(labels(b)) AS l2, type(r) AS rel_type,
count(*) as count
CALL apoc.create.vNode([l],{name:l}) yield node as a
CALL apoc.create.vNode([l2],{name:l2}) yield node as b
CALL apoc.create.vRelationship(a,rel_type,{name:rel_type, count:count},b)
YIELD rel
RETURN *;

Clubs without country
MATCH (club:Club)
WHERE NOT (club)-[:PART_OF]->()
RETURN club
+=====================================================================+
|club |
+=====================================================================+
|{name: Unknown, id: /unknown/startseite/verein/75} |
+---------------------------------------------------------------------+
|{country: Monaco, name: AS Monaco, id: /monaco/startseite/verein/162}|
+---------------------------------------------------------------------+

Deleting data - SQL
# drop table countries;
ERROR: cannot drop table countries because other objects depend on
it
DETAIL: constraint playersfk on table players depends on table
countries
HINT: Use DROP ... CASCADE to drop the dependent objects too.

DELETE country
org.neo4j.kernel.api.exceptions.TransactionFailureException: Node
record Node[11306,used=false,rel=24095,prop=-1,labels=Inline(0x0:
[]),light] still has relationships
Deleting data - Cypher

DETACH DELETE country
Deleted 198 nodes, deleted 5071 relationships, statement executed
in 498 ms.
Deleting data - Cypher

Optimising queries
‣ Use EXPLAIN/PROFILE to see what your
queries are doing under the covers
‣ Index the starting points of queries
‣ Reduce work in progress of intermediate
parts of the query where possible
‣ Look at the warnings in the Neo4j browser -
they are often helpful!

Optimising queries - useful links
‣ Tuning Your Cypher
https://www.youtube.com/watch?v=tYtyoYcd_e8
‣ Neo4j 2.2 Query Tuning
http://neo4j.com/blog/neo4j-2-2-query-tuning/
‣ Ask for help on Stack Overflow/Neo4j Slack
http://neo4j-users-slack-invite.herokuapp.com

‣ New in Neo4j 3.0.0!
Procedures

‣ New in Neo4j 3.0.0!
‣ We’ve already seen an example!
CALL db.labels()
‣ Michael Hunger has created a set of
procedures (APOC) at:
https://github.com/jexp/neo4j-apoc-procedures
Procedures

WITH "https://api.github.com/search/repositories?q=neo4j"
AS githubUri
CALL apoc.load.json(githubUri)
YIELD value AS document
UNWIND document.items AS item
RETURN item.full_name, item.watchers_count, item.forks
ORDER BY item.forks DESC
Querying github

+------------------------------------------------------------------------+
| item.full_name | item.watchers_count | item.forks |
+------------------------------------------------------------------------+
| "neo4j/neo4j" | 2472 | 872 |
| "spring-projects/spring-data-neo4j" | 403 | 476 |
| "neo4j-contrib/developer-resources" | 106 | 295 |
| "neo4jrb/neo4j" | 1014 | 190 |
| "jadell/neo4jphp" | 507 | 140 |
| "thingdom/node-neo4j" | 780 | 127 |
| "aseemk/node-neo4j-template" | 176 | 91 |
| "jimwebber/neo4j-tutorial" | 268 | 87 |
| "rickardoberg/neo4j-jdbc" | 33 | 68 |
| "FaKod/neo4j-scala" | 194 | 64 |
+------------------------------------------------------------------------+
Querying github

Questions? :-)
Mark Needham
mark@neo4j.com
@markhneedham
https://github.com/neo4j-meetups/cypher-for-sql-developers

Intro to Cypher for the SQL Developer

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