Data Modification Statements
The GSQL language provides full support for vertex and edge insertion, deletion, and attribute update.
Modifications to the graph data do not take effect until the entire query is completed (committed). If one step needs to see the changes of an earlier step, you must separate the work into separate queries run in sequence. |
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.
The GSQL DELETE
operation is a cascading deletion.
If a vertex is deleted, then all edges which connect to it are automatically deleted as well.
Syntax
queryBodyDeleteStmt := DELETE alias FROM pathPattern [whereClause]
The FROM
clause in the DELETE
statement follows the same rules as those in the FROM
clause in a SELECT
statement.
However, the FROM
clause in the DELETE
statement only supports 1-hop, instead of multiple hops in the SELECT
statement.
The WHERE
clause can filter the items in the path pattern.
Examples
Below are two examples, one for deleting vertices and one for deleting edges.
CREATE QUERY delete_ex() FOR GRAPH Work_Net {
// Delete all "Person" vertices with location equal to "us"
S = {Person.*};
DELETE s FROM S:s
WHERE s.location_id == "us";
}
CREATE QUERY delete_ex_2() FOR GRAPH Work_Net {
// Delete all "Works_For" edges where the person's location is "us"
S = {Person.*};
DELETE e FROM S:s -(Works_For:e)- Company:t
WHERE s.location_id == "us";
}
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 and the Works_For
edges for persons in the US.
When the initial Work_Net
test data loaded, there are 5 persons and 9 Works_For edges for locationId = "us".
If query delete_ex2
is run, there are 5 persons but 0 Works_For
edges.
Next, if the deleteEx query is run, the works_at_US
query then finds 0 persons and 0 Works_For
edges.
CREATE QUERY count_at_location(STRING loc) FOR GRAPH Work_Net {
SetAccum<EDGE> @@sel_edge;
Start = {Person.*};
SV = SELECT s FROM Start:s
WHERE s.location_id == loc;
PRINT SV.size() AS num_vertices;
SE = SELECT s FROM Start:s -(Works_For:e)- Company:t
WHERE s.location_id == loc
ACCUM @@sel_edge += e;
PRINT @@sel_edge.size() AS num_edges;
}
Below are the results of the queries in sequence:
RUN QUERY count_at_location("us")
RUN QUERY delete_ex2()
RUN QUERY count_at_location("us")
RUN QUERY deleteEx()
RUN QUERY count_at_location("us")
// Before any deletions
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [
{"numVertices": 5},
{"numEdges": 9}
]
}
// Delete edges
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": []
}
// After deleting edges
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [
{"numVertices": 5},
{"numEdges": 0}
]
}
// Delete vertices
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": []
}
// After deleting vertices
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [
{"numVertices": 0},
{"numEdges": 0}
]
}
DML-sub DELETE
Statement
DML-sub DELETE
is a DML-sub statement 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.
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 GSQL DELETE operation is a cascading deletion. If a vertex is deleted, then all edges which connect to it are automatically deleted as well.
The |
Syntax
dmlSubDeleteStmt := DELETE "(" alias ")"
Examples
The following example uses and modifies the graph data for Social_Net
.
DELETE
within ACCUM
vs. POST-ACCUM
CREATE QUERY delete_posts(VERTEX<Person> seed) FOR GRAPH Social_Net {
// Remove any post vertices posted by the given user
start = {seed};
/* Best practice is to delete a vertex in a POST-ACCUM, which only
occurs once for each vertex v, guaranteeing that a vertex is not
deleted more than once */
post_accum_deleted_posts = SELECT v FROM start -(Posted>:e)- Post:v
POST-ACCUM DELETE (v);
/* Possible, but not recommended as the DML-sub DELETE statement occurs
once for each edge of the vertex v */
accum_deleted_posts = SELECT v FROM start -(Posted>:e)- Post:v
ACCUM DELETE (v);
}
// Need a separate query to display the results, because deletions don't take effect during the query.
CREATE QUERY select_user_posts(VERTEX<Person> seed) FOR GRAPH Social_Net {
start = {seed};
user_posts = SELECT v FROM start -(Posted>:e)- Post:v;
PRINT user_posts;
}
For example, the following sequence of select_user_posts
and delete_posts
queries
RUN QUERY select_user_posts("person3")
RUN QUERY delete_posts("person3")
RUN QUERY select_user_posts("person3")
will produce the following result:
// Before the deletion
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [{"userPosts": [{
"v_id": "2",
"attributes": {
"postTime": "2011-02-03 01:02:42",
"subject": "query languages"
},
"v_type": "post"
}]}]
}
// Deletion; no output results requested at this point
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": []
}
// After the deletion
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [{"userPosts": []}]
}
INSERT INTO
Statement
The INSERT INTO
statement adds edges or vertices to the graph.
When the ID value(s) for the inserted vertex/edge match those of an existing vertex/edge, the new values will overwrite the old values.
To insert an edge, its endpoint vertices must already exist, either before 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-sub statement.
Like any other data modification in a query, the insertion does not take effect until the entire query is completed.
insertStmt := insertVertexStmt | insertEdgeStmt
insertVertexStmt := INSERT INTO (vertexType | name)
["(" PRIMARY_ID ["," attrName]* ")"]
VALUES "(" ( "_" | expr ) ["," ("_" | expr)]*] ")"
insertEdgeStmt := INSERT INTO (edgeType | EDGE name)
["("
FROM "," TO “,”
[(DISCRIMINATOR "(" attrName ("," attrName)* ")") ]
")"]
VALUES "(" ( "_" | expr ) [vertexType]
["," ( "_" | expr ) [vertexType] ["," ("_" | expr)]*] ")"
There are two options for specifying the attributes of the vertex or edge type for the values provided:
-
Provide a value for the ID(s) and then each attribute, in the canonical order for the vertex or edge type. In this case, it is not necessary to explicitly name the attributes, since it is assumed that every attribute is being referenced, in order.
INSERT with implicit attribute namesINSERT INTO vertex_or_edge_type VALUES (full_list_of_parameter_values)
-
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 beFROM
andTO
.INSERT with explicit attribute namesINSERT INTO vertex_type (PRIMARY_ID, specified_attributes) VALUES (ID, values_for_specified_attributes) INSERT INTO edge_type (FROM, TO, specified_attributes) VALUES (value_for_from_vertex, value_for_to_vertex, (1) values_for_specified_attributes)
1 value_for_from_vertex
andvalue_for_to_vertex
can either be the ID of the vertex followed by the vertex type, separated by a space or a vertex variable.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 following query illustrates query-body level INSERT
statements: insert new Company
vertices and Works_For
edges into the Works_Net
graph.
CREATE QUERY insert_ex(STRING name, STRING name2, STRING name3, STRING comp) FOR GRAPH Work_Net {
/* Vertex insertion
Adds 2 'Company' vertices. One is located in the USA, and a sister company in Japan.
Company:
Company(PRIMARY_ID client_id STRING, id STRING, country STRING) */
INSERT INTO Company VALUES ( comp, comp, "us" );
INSERT INTO Company (PRIMARY_ID, country) VALUES ( comp + "_jp", "jp" );
/* Edge insertion
Adds a 'Works_For' edge from person 'name' to the company 'comp', filling in default
values for startYear (0), startMonth (0), and fullTime (false).
Works_For:
Works_For(FROM person, TO company, startYear INT, startMonth INT, fullTime BOOL) */
INSERT INTO Works_For VALUES (name Person, comp Company, _, _, _);
/* Adds a 'Works_For' edge from person 'name2' to the company 'comp', filling in
default values for startMonth (0), but specifying values for startYear and
fullTime. */
INSERT INTO Works_For (FROM, TO, start_year, full_time) VALUES (name2 Person, comp Company, 2017, true);
/* Adds a 'Works_For' edge from person 'name3' to the company 'comp', filling in
default values for startMonth (0), and fullTime (false) but specifying a value
for startYear (2017). */
INSERT INTO Works_For (FROM, TO, start_year) VALUES (name3 Person, comp Company, 2000 + 17);
}
The following query can be used to check the effect of the previous query.
Prior to running insertEx
, running whoWorksForCompany("gsql")
will find 0 companies
called "gsql"
and 0 Works_For
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.
CREATE QUERY who_works_for_company(STRING comp) FOR GRAPH Works_Net {
SetAccum<EDGE> @@set_edge;
Comps = {Company.*};
PRINT Comps[Comps.id]; // output api v2
Pers = {Person.*};
S = SELECT s
FROM Pers:s -(Works_For:e)- :t
WHERE t.id == comp
ACCUM @@set_edge += e;
PRINT @@set_edge;
}
To insert an edge with a discriminator value specified, use the DISCRIMINATOR
keyword to specify the discriminator attributes and specify the values in order.
For example, the following statement inserts an edge between two vertices with the discriminator values being 2019 and 01, respectively.
INSERT INTO Study_At (FROM, TO, DISCRIMINATOR(class_year, class_month))
VALUES ("Alice" Person, "CMU" University, (2019, 01));
DML-sub INSERT
The following example shows a DML-sub level INSERT. Because the statement applies to all companies, several vertices will be inserted.
CREATE QUERY add_new_child_company(STRING name) FOR GRAPH Work_Net {
// Adds a child company of a given company name. The new child company is in japan
all_companies = {Company.*};
X = SELECT s
FROM all_companies:s
WHERE s.id == name
ACCUM
INSERT INTO Company VALUES ( name + "_jp", name + "_jp", "jp" );
}
// Adds separate query to list the companies, before and after the insertion
CREATE QUERY list_company_names(STRING country_filter) FOR GRAPH Works_Net {
all_companies = {Company.*};
C = SELECT s
FROM all_companies:s
WHERE s.country == country_filter;
PRINT C.size() AS num_companies;
PRINT C;
}
Example
The following queries add a child company in Japan to the US-based company company3
.
List all the Japan-based companies before and after the insertion.
RUN QUERY list_company_names("jp")
RUN QUERY add_new_child_company("company4")
RUN QUERY list_company_names("jp")
# Before insertion
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [
{"numCompanies": 1},
{"C": [{
"v_id": "company3",
"attributes": {
"country": "jp",
"id": "company3"
},
"v_type": "company"
}]}
]
}
# insert company "company4_jp"
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": []
}
# after insertion
{
"error": false,
"message": "",
"version": {
"edition": "developer",
"schema": 0,
"api": "v2"
},
"results": [
{"numCompanies": 2},
{"C": [
{
"v_id": "company3",
"attributes": {
"country": "jp",
"id": "company3"
},
"v_type": "company"
},
{
"v_id": "company4_jp",
"attributes": {
"country": "jp",
"id": "company4_jp"
},
"v_type": "company"
}
]}
]
}
UPDATE
Statement
The UPDATE
statement updates the attributes of vertices or edges.
Syntax
updateStmt := UPDATE alias FROM pattern SET dmlSubStmtList [whereClause]
pattern := (vertexPattern | edgePattern)
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
statement.
In the SET
clause, the dmlSubStmtList
contains 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 vertex set or edge set.
Examples
UPDATE
statement exampleCREATE QUERY update_ex() FOR GRAPH Work_Net {
// This query changes all "Person" vertices with location equal to "us" to "USA"
S = {Person.*};
UPDATE s FROM S:s
SET s.location_id = "USA", // simple base type attribute
s.skill_list = [1,2,3] // collection-type attribute
WHERE s.location_id == "us";
// The update cannot become effective within this query, so PRINT S still show "us".
PRINT S;
}
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.
Updating a vertex’s attribute value in an |
The query below uses a SELECT
statement instead of an UPDATE
statement and performs the same update as the query above.
CREATE QUERY update_ex2() FOR GRAPH Work_Net {
S = {Person.*};
X = SELECT s
FROM S:s
WHERE S.location_id == "USA"
POST-ACCUM S.location_id = "us",
S.skill_list = [3,2,1];
PRINT S;
}
Assignment statements
In addition to UPDATE
statements and SELECT
statements, a simple assignment statement at the query-body level can be used to update the attribute value of a single vertex or edge, if the vertex or edge has been assigned to a variable or parameter.
// Change the given person's location
CREATE QUERY update_by_assignment(VERTEX<Person> v, STRING new_location)
FOR GRAPH Work_Net {
v.location_id = new_location;
}