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Comparison Between SQL and nGQL

Conceptual Comparisons

Items SQL nGQL
vertex \ vertex
edge \ edge
vertex type \ tag
edge type \ edge type
vertex identifier primary key vid
edge identifier composite primary key src, dst, rank
column column properties of vertices or edges
row row one vertex or edge

Syntax Comparisons

Data Definition Language (DDL)

Data Definition Language (DDL) can be used to define a database schema. DDL statements create and modify the structure of a database.

Items SQL nGQL
Create (graph) database CREATE DATABASE <database_name> CREATE SPACE <space_name>
Show (graph) database SHOW DATABASES SHOW SPACES
Use (graph) database USE <database_name> USE <space_name>
Drop (graph) database DROP DATABASE <database_name> DROP SPACE <space_name>
Alter (graph) database ALTER DATABASE <database_name> alter_option \
Create tags/edges \ CREATE TAG | EDGE <tag_name>
Create a table CREATE TABLE <tbl_name> (create_definition,...) \
Show columns SHOW COLUMNS FROM <tbl_name> \
Show tags/edges \ SHOW TAGS | EDGES
Describe tags/edge \ DESCRIBE TAG | EDGE <tag_name | edge_name>
Alter a tag/edge \ ALTER TAG | EDGE <tag_name | edge_name>
Alter a table ALTER TABLE <tbl_name> \

Index

Items SQL nGQL
Create index CREATE INDEX CREATE {TAG | EDGE} INDEX
Drop index DROP INDEX DROP {TAG | EDGE} INDEX
Show index SHOW INDEX FROM SHOW {TAG | EDGE} INDEXES
Rebuild index ANALYZE TABLE REBUILD {TAG | EDGE} INDEX <index_name> [OFFLINE]

Data Manipulation Language (DML)

Data Manipulation Language (DML) is used to manipulate data in a database.

Items SQL nGQL
Insert data INSERT IGNORE INTO <tbl_name> [(col_name [, col_name] ...)] {VALUES | VALUE} [(value_list) [, (value_list)] INSERT VERTEX <tag_name> (prop_name_list[, prop_name_list]) {VALUES | VALUE} vid: (prop_value_list[, prop_value_list])
INSERT EDGE <edge_name> ( <prop_name_list> ) VALUES | VALUE <src_vid> -> <dst_vid>[@<rank>] : ( <prop_value_list> )
Query data SELECT GO, FETCH
Update data UPDATE <tbl_name> SET field1=new-value1, field2=new-value2 [WHERE Clause] UPDATE VERTEX <vid> SET <update_columns> [WHEN <condition>]
UPDATE EDGE <edge> SET <update_columns> [WHEN <condition>]
Delete data DELETE FROM <tbl_name> [WHERE Clause] DELETE EDGE <edge_type> <vid> -> <vid>[@<rank>] [, <vid> -> <vid> ...]
DELETE VERTEX <vid_list>
Join data JOIN |

Data Query Language (DQL)

Data Query Language (DQL) statements are used for performing queries on the data. This section shows how you can query data with SQL statements and nGQL statements.

SELECT
 [DISTINCT]
 select_expr [, select_expr] ...
 [FROM table_references]
 [WHERE where_condition]
 [GROUP BY {col_name | expr | position}]
 [HAVING  where_condition]
 [ORDER BY {col_name | expr | position} [ASC | DESC]]

GO [[<M> TO] <N> STEPS ] FROM <node_list>
 OVER <edge_type_list> [REVERSELY] [BIDIRECT]
 [WHERE where_condition]
 [YIELD [DISTINCT] <return_list>]
 [| ORDER BY <expression> [ASC | DESC]]
 [| LIMIT [<offset_value>,] <number_rows>]
 [| GROUP BY {col_name | expr | position} YIELD <col_name>]

<node_list>
   | <vid> [, <vid> ...]
   | $-.id

<edge_type_list>
   edge_type [, edge_type ...]

<return_list>
    <col_name> [AS <col_alias>] [, <col_name> [AS <col_alias>] ...]

Data Control Language (DCL)

Data Control Language (DCL) includes commands such as GRANT and REVOKE that mainly deals with the rights, permissions, and other controls of the database system.

Items SQL nGQL
Create user CREATE USER CREATE USER
Drop user DROP USER DROP USER
Change password SET PASSWORD CHANGE PASSWORD
Grant privilege GRANT <priv_type> ON [object_type] TO <user> GRANT ROLE <role_type> ON <space> TO <user>
Revoke privilege REVOKE <priv_type> ON [object_type] TO <user> REVOKE ROLE <role_type> ON <space> FROM <user>

Data Model

The queries are based on the data model below:

MySQL

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Nebula Graph

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CRUD

This section describes how to create (C), read (R), update (U), and delete (D) data with SQL and nGQL statements.

Inserting Data

mysql> INSERT INTO player VALUES (100, 'Tim Duncan', 42);

nebula> INSERT VERTEX player(name, age) VALUES 100: ('Tim Duncan', 42);

Querying Data

Find the player whose id is 100 and output the name property:

mysql> SELECT player.name FROM player WHERE player.id = 100;

nebula> FETCH PROP ON player 100 YIELD player.name;

Updating Data

mysql> UPDATE player SET name = 'Tim';

nebula> UPDATE VERTEX 100 SET player.name = "Tim";

Deleting Data

mysql> DELETE FROM player WHERE name = 'Tim';

nebula> DELETE VERTEX 121;
nebula> DELETE EDGE follow 100 -> 200;

Sample Queries

Query 1

Find players who are younger than 36.

mysql> SELECT player.name
FROM player
WHERE player.age < 36;

The query in nGQL is a bit different because you must create an index before filtering a property. For more information, see Index Doc.

nebula> CREATE TAG INDEX player_age ON player(age);
nebula> REBUILD TAG INDEX player_age OFFLINE;
nebula> LOOKUP ON player WHERE player.age < 36;

Query 2

Find Tim Duncan and list all the teams that he served.

mysql> SELECT a.id, a.name, c.name
FROM player a
JOIN serve b ON a.id=b.player_id
JOIN team c ON c.id=b.team_id
WHERE a.name = 'Tim Duncan';

nebula> CREATE TAG INDEX player_name ON player(name);
nebula> REBUILD TAG INDEX player_name OFFLINE;
nebula> LOOKUP ON player WHERE player.name == 'Tim Duncan' YIELD player.name AS name | GO FROM $-.VertexID OVER serve YIELD $-.name, $$.team.name;

Query 3

Find Tim Duncan's teammates.

mysql> SELECT a.id, a.name, c.name
FROM player a
JOIN serve b ON a.id=b.player_id
JOIN team c ON c.id=b.team_id
WHERE c.name IN (SELECT c.name
FROM player a
JOIN serve b ON a.id=b.player_id
JOIN team c ON c.id=b.team_id
WHERE a.name = 'Tim Duncan');

In nGQL we use pipes to pass the output of the previous statement as the input for the next statement.

nebula> GO FROM 100 OVER serve YIELD serve._dst AS Team | GO FROM $-.Team OVER serve REVERSELY YIELD $$.player.name;
Last update: April 8, 2021