Data Modification Statements

The GSQL language provides full support for vertex and edge insertion, deletion, and attribute update is provided. Therefore, the language is more than just a "query" language.

Query-body DELETE Statement

The query-body DELETE statement deletes a given set of edges or vertices. This statement can only be used as a query-body statement. (Deletion at the DML-sub level is served by the DML-sub DELETE statement, described next.

The vertexSet and edgeSet terms in the FROM clause follow the same rules as those in the FROM clause in a SELECT statement. The WHERE clause can filter the items in the vertexSet or edgeSet.Below are two examples, one for deleting vertices and one for deleting edges.

The following query can be used to observe the effect of the delete statements. This query counts the person vertices who work in the US ("us") and the worksFor edges for persons in the US. When the initial workNet test data loaded, there are 5 persons and 9 worksFor edges for locationId = "us". If query deleteEx2 is run, the worksAtUS query will then find the 5 persons but 0 worksFor edges. Next, if the deleteEx query is run, the worksAtUS query will then find 0 persons and 0 worksFor edges.

For example, the following sequence of countAtLocation, deleteEx2, and deleteEx queries

will produce the following result:

DML-sub DELETE Statement

DML-sub DELETE is a DML-substatement which deletes one vertex or edge each time it is called. (Deletion at the query-body level is served by the Query-body DELETE statement described above.) In practice, this statement resides within the body of a SELECT...ACCUM/POST-ACCUM clause, so it is called once for each member of a selected vertex set or edge set.

The following example uses and modifies the graph data for socialNet.

For example, the following sequence of selectUserPosts and deletePosts queries

will produce the following result:

INSERT INTO Statement

The INSERT INTO statement adds edges or vertices to the graph. However, if the ID value(s) for the inserted vertex/edge match those of an existing vertex/edge, then the new values will overwrite the old values. To insert an edge, its endpoint vertices must already exist, either prior to running the query or inserted earlier in that query.The INSERT INTO statement can be used as a query-body-level statement or a DML-substatement.

The formal syntax is complex because it encompasses several options, and even so, it requires additional explanation. The first name symbol is the vertex type or edge type. The user then has two options:

1) Provide a value for the ID(s) and then each attribute, in the canonical order for the vertex or edge type. This format is similar to that of a LOAD statement. In this case, it is not necessary to explicitly name the attributes, since it is assumed that every one is being referenced, in order.

2) Name the specific attributes to be set, and then provide a corresponding list of values. The attributes can be in any order, with the exception that the IDs must come first. That is, to insert a vertex, the first attribute name must be PRIMARY_ID. To insert an edge, the first two attribute names must be FROM and TO.

For each attribute value, provide either an expression expr or "_", which means the default value for that attribute type. The optional name which follows the first two (id) values is to specify the source vertex type and target vertex type, if the edge type had been defined with wildcard vertex types.

Query-Body INSERT

The query insertEx illustrates query-body level INSERT statements: insert new company vertices and worksFor examples into the workNet graph.

The query whoWorksForCompany can be used to check the effect of query insertEx. Prior to running insertEx, running whoWorksForCompany("gsql") will find 0 companies called "gsql" and 0 worksFor edges for company "gsql". If we then run the query insertEx("tic", "tac", "toe", "gsql"), then insertEx("gsql") will find a company called "gsql" and another one called "gsql_jp". Moreover, it will find 3 edges, tic, tac, and toe, with different values for the startMonth, startYear, and fullTime parameters.

DML-sub INSERT

The following example show a DML-sub level INSERT. Because the statement applies to allCompanies, several vertices will be inserted.

Example: Add a child company in Japan to US-based company company3. List all the Japan-based companies before and after the insertion.

UPDATE Statement

The UPDATE statement updates the attribute of each vertex or edge in a vertex set or edge set, respectively, with new attribute values.

The set of vertices or edges to update is described in the FROM clause, following the same rules as the FROM clause in a SELECT block. In the SET clause, the DMLSubStmtList may contain assignment statements to update the attributes of a vertex or edge. Both simple base type attributes and collection type attributes can be updated. These assignment statements use the vertex or edge aliases declared in the FROM clause. The optional WHERE clause supports boolean conditions to filter the items in the vertexSet or edgeSet.

The UPDATE statement can only be used as a query-body-level statement. However, DML-sub level updates are still possible by using other statement types. A vertex attribute's value can be updated within the POST-ACCUM clause of a SELECT block by using the assignment operator (=); An edge attribute's value can be updated within the ACCUM clause of a SELECT block by using the assignment operator. In fact, the UPDATE statement is equivalent to a SELECT statement with ACCUM and/or POST-ACCUM to update the vertex or edge attribute values. Below is an example.

The query below uses the SELECT statement instead of the UPDATE statement, but is functional similar to the query above. Query updateEx2 reverses the locationId change made by updateEx (changing the location back to "us" from "USA").

Below is an example of an edge update with two attribute changes, including an incremental change (e.startYear = e.startYear + 1):

Other Update Methods

In addition to the above UPDATE statement and SELECT statement, a simple assignment statement at the query-body level can be used to update the attribute value of a single vertex/edge, if the vertex/edge has been assigned to a variable or parameter.