Statements

Table of Contents

1. Statements (Overview)
2. CREATE Statement
3. DROP Statement
4. SET Statement
5. (IN|UP)SERT Statement
6. DELETE Statement

Statements (Overview)

In addition to queries, gSQL++ needs to support statements for a) managing the definition of graphs, and b) for controlling the context used in query compilation & evaluation.

CREATE Statement

The CREATE statement is used for creating dataverses and other persistent artifacts within a dataset. In Graphix, if users want to create a AsterixDB managed graph whose metadata / name is persisted across requests, they would use the CREATE GRAPH statement as opposed to defining a temporary graph using the WITH GRAPH clause.

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CREATE Statement

CREATE GRAPH Statement

Graph Constructor

Vertex Constructor

Vertex Constructor Detail

Vertex Definition

Edge Constructor

Edge Constructor Detail

Edge Definition

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A graph in Graphix is specified by using the graph constructor production. A graph constructor is used to specify the schema of a graph containing one or more vertices, and zero or more edges.

To specify a vertex in a graph schema, the vertex constructor production is used. A vertex constructor consists of a) a single label (specified using a vertex pattern), b) a primary key, and c) a vertex body specified after the AS keyword. The edge constructor production is used to specify an edge in a graph schema, and consists of a) a source vertex label (specified using a vertex pattern), b) a destination vertex label (again, specified using a vertex pattern), c) an edge label (specified using an edge pattern), d) a direction (using arrows, again from the edge pattern), e) a source key, f) a destination key, and g) an edge body. The source key and destination key will be used when connecting the edge itself to its source vertex and destination vertex.

An example CREATE GRAPH is given below:

CREATE GRAPH Gelp.GelpGraph AS

    VERTEX (:Business)
        PRIMARY KEY (business_id)
        AS Gelp.Businesses,

    VERTEX (:User)
        PRIMARY KEY (user_id)
        AS Gelp.Users,

    VERTEX (:Review)
        PRIMARY KEY (review_id)
        AS ( 
            FROM    
                Gelp.Reviews R
            WHERE   
                R.review_time IS NOT UNKNOWN
            SELECT VALUE 
                R 
        ),
    
    EDGE (:Review)-[:ABOUT]->(:Business)
        SOURCE KEY       (review_id)
        DESTINATION KEY  (business_id)
        AS ( 
            FROM    
                Gelp.Reviews R
            WHERE   
                R.review_time IS NOT UNKNOWN
            SELECT  
                R.review_id,
                R.business_id 
        ),

    EDGE (:Review)-[:MADE_BY]->(:User)
        SOURCE KEY       (review_id)
        DESTINATION KEY  (user_id)
        AS ( 
            FROM    
                Gelp.Reviews R
            WHERE   
                R.review_time IS NOT UNKNOWN
            SELECT  
                R.review_id,
                R.user_id 
        ),

    EDGE (:User)-[:FRIENDS_WITH]->(:User)
        SOURCE KEY       (user_id)
        DESTINATION KEY  (friend)
        AS ( 
            FROM    
                Gelp.Users U,
                U.friends F
            SELECT  
                F         AS friend,
                U.user_id AS user_id 
        );

Although vertex and edge patterns are used to specify our graph schema, the following constraints are imposed on any defined graph:

1. A vertex must have exactly one label.
2. An edge must have exactly one label.
3. The source vertex of an edge must have exactly one label.
4. The destination vertex of an edge must have exactly one label.
5. An edge must be directed.
6. An edge must reference a vertex that is defined within that schema.

DROP Statement

The DROP statement is the inverse of the CREATE statement, and is used to drop dataverses, datatypes, indexes, functions, synonyms, and graphs.

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DROP GRAPH Statement

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SET Statement

The SET statement allows users to give additional context to both Graphix and the AsterixDB optimizer. For AsterixDB specific parameters, see here. For Graphix specific parameters, see here.

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SET Statement

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(IN|UP)SERT Statement

The INSERT statement is used to insert new data into a dataset. The UPSERT statement is “add or replace” data into / from a dataset. These statements remain unchanged from SQL++.

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INSERT / UPSERT Statement

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gSQL++ does not directly support the creation of vertices and edges, as each vertex and edge body represents a view of your logical model. Such an action is akin to inserting a record into a SQL++ (or SQL) view– inserting new vertices or edges is an action that depends on the element bodies composing your graph schema. Users can still, however, leverage gSQL++ to aid in modifying the vertices and edges in your graph. The example below utilizes an anti-join to locate users that should have a FRIENDS_WITH edge between them, and then adds to the Friends dataset if no such edge is found:

INSERT INTO Friends
    FROM    
        GRAPH GelpGraph
            (u1:User)
    LET     
        targetFriendID = 5
    WHERE   
        u1.user_id NOT IN (
            FROM    
                GRAPH GelpGraph
                    (uu1:User)-[:FRIENDS_WITH]->(uu2:User)
            WHERE   
                uu1 = u1 AND 
                uu2.user_id = targetFriendID 
            SELECT VALUE 
                uu1.user_id
        )
    SELECT  
        u1.user_id     AS user_id,
        targetFriendID AS friend;

DELETE Statement

The DELETE statement is used to delete data from a target dataset. This statement remains unchanged from SQL++.

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DELETE Statement

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gSQL++ also does not directly support the deletion of vertices and edges. Users can, however, use a gSQL++ query to locate the exact record(s) they want to delete. Suppose that we want to delete all users that have made reviews for a fake business. We can accomplish this deletion using a correlated sub-query:

DELETE FROM Users AS u
    WHERE 
        EXISTS (
            FROM
                GRAPH GelpGraph
                    (gu:User)-(:Review)-(gb:Business)
            WHERE   
                "fake" IN gb.annotations AND
                u = gu
            SELECT  
                1
        );