Control Flow Statements

The GSQL Query Language includes a comprehensive set of control flow statements to empower sophisticated graph traversal and data computation: IF/ELSE, CASE, WHILE, and FOREACH.

Differences in Block Syntax

Note that any of these statements can be used as a query-body statement or as a DML-sub level statement.

If the control flow statement is at the query-body level, then its block(s) of statements are query-body statements ( queryBodyStmts ). In a queryBodyStmts block, each individual statement ends with a semicolon, so there is always a semicolon at the end.

If the control flow statement is at the DML-sub level, then its block(s) of statements are DML-sub statements ( dmlSubStmtList ). In a dmlSubStmtList block, a comma separates statements, but there is no punctuation at the end.

For more detailed general examples of the difference between query-body statements and DML-sub statements, see statement types.

`IF` Statement

The IF statement provides conditional branching: execute a block of statements ( queryBodyStmts or dmlSubStmtList ) only if a given condition is true. The IF statement allows for zero or more ELSE-IF clauses, followed by an optional ELSE clause. The IF statement can be used either at the query-body level or at the DML-sub-statement level. (See the note about differences in block syntax.)

Syntax

IF syntax

queryBodyIfStmt := IF condition THEN queryBodyStmts
                 [ELSE IF condition THEN queryBodyStmts ]*
                 [ELSE queryBodyStmts ] END
dmlSubIfStmt :=    IF condition THEN dmlSubStmtList
                 [ELSE IF condition THEN dmlSubStmtList ]*
                 [ELSE dmlSubStmtList ] END

If an IF condition is not true, then the flow proceeds to the next ELSE IF condition. When a true condition is encountered, its corresponding block of statements is executed, and then the IF statement terminates (skipping any remaining ELSE-IF or ELSE clauses). If an ELSE clause is present, its block of statements are executed if none of the preceding conditions are true. Overall, the functionality can be summarized as "execute the first block of statements whose conditional test is true."

IF semantics

// if then
IF x == 5 THEN y = 10; END;      # y is assigned to 10 only if x is 5.

// if then else
IF x == 5 THEN y = 10;       # y is 10 only if x is 5.
ELSE y = 20; END;            # y is 20 only if x is NOT 5.

// if with ELSE IF
IF x == 5 THEN y = 10;       # y is 10 only if x is 5.
ELSE IF x == 7 THEN y = 5;   # y is 5  only if x is 7.
ELSE y = 20; END;            # y is 20 only if x is NOT 5 and NOT 7.

Examples

Query
Results

This query counts the number of friends a person has, and optionally include coworkers in that count

Simple IF-ELSE at query-body level

CREATE QUERY count_friends_of2(VERTEX<Person> seed, BOOL include_coworkers) FOR GRAPH Friend_Net
{
    SumAccum<INT> @@num_friends = 0;
    start = {seed};

    IF include_coworkers THEN
        friends = SELECT v FROM start -((Friend | Coworker):e)- :v
            ACCUM @@num_friends +=1;
    ELSE
        friends = SELECT v FROM start -(Friend:e)- :v
            ACCUM @@num_friends +=1;
    END;
    PRINT @@num_friends, include_coworkers;
}

RUN QUERY count_friends_of2("person2", false)
{
  "error": false,
  "message": "",
  "version": {
    "schema": 0,
    "edition": "enterprise",
    "api": "v2"
  },
  "results": [{
    "@@num_friends": 2,
    "include_coworkers": false
  }]
}

Query
Results

This query uses a more advanced activity calculation, taking into account number of posts and number of likes that a user made.

CREATE QUERY calculate_in_depth_activity(VERTEX<Person> seed) FOR GRAPH Social_Net
{
    SumAccum<INT> @@number_posts = 0;
    SumAccum<INT> @@number_likes = 0;
    start = {seed};
    result = SELECT post_vertex FROM start -(Posted>:e)- :post_vertex
        ACCUM @@number_posts += 1;
    result = SELECT liked_post FROM start -(Liked>:e)- :liked_post
        ACCUM @@number_likes += 1;

    IF @@number_posts < 2 THEN
        IF @@number_likes < 1 THEN
            PRINT "Not very active";
        ELSE
            PRINT "Semi-active";
        END;
    ELSE IF @@number_posts < 3 THEN
        IF @@number_likes < 2 THEN
            PRINT "Semi-active";
        ELSE
            PRINT "Active";
        END;
    ELSE
        PRINT "Very active";
    END;
}

RUN QUERY calculate_in_depth_activity("person1")
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"Semi-active": "Semi-active"}]
}

`CASE` Statement

The CASE statement provides conditional branching: execute a block of statements only if a given condition is true. CASE statements can be used as query-body statements or DML-sub-statements. (See note about differences in block syntax.)

Syntax

CASE syntax

queryBodyCaseStmt := CASE  (WHEN condition THEN queryBodyStmts)+ [ELSE queryBodyStmts] END
               | CASE expr (WHEN constant  THEN queryBodyStmts)+ [ELSE queryBodyStmts] END
dmlSubCaseStmt := CASE     (WHEN condition THEN dmlSubStmtList)+ [ELSE dmlSubStmtList] END
               | CASE expr (WHEN constant  THEN dmlSubStmtList)+ [ELSE dmlSubStmtList] END

One CASE statement contains one or more WHEN-THEN clauses, each WHEN presenting one expression. The CASE statement may also have one ELSE clause whose statements are executed if none of the preceding conditions are true.

There are two syntax of the CASE statement: one equivalent to an if-else statement, and the other is structured like a switch statement. The if-else version evaluates the boolean condition within each WHEN clause and executes the first block of statements whose condition is true. The optional concluding ELSE clause is executed only if all WHEN clause conditions are false.

The switch version evaluates the expression following the keyword WHEN and compares its value to the expression immediately following the keyword CASE. These expressions do not need to be boolean; the CASE statement compares pairs of expressions to see if their values are equal. The first WHEN-THEN clause to have an expression value equal to the CASE expression value is executed; the remaining clauses are skipped. The optional ELSE clause is executed only if no WHEN clause expression has a value matching the CASE value.

CASE Semantics

STRING drink = "Juice";

// CASE statement: if-else version
CASE
  WHEN drink == "Juice" THEN @@calories += 50
  WHEN drink == "Soda"  THEN @@calories += 120
  ...
  ELSE @@calories = 0       // Optional else-clause
END
// Since drink = "Juice", 50 will be added to calories

// CASE statement: switch version
CASE drink
  WHEN "Juice" THEN @@calories += 50
  WHEN "Soda"  THEN @@calories += 120
  ...
  ELSE  @@calories = 0    // Optional else-clause
END
// Since drink = "Juice", 50 will be added to calories

Examples

Query
Results

This query tallies male and female friends of the starting vertex.

CREATE QUERY count_gender_of_friends(VERTEX<Person> seed) FOR GRAPH Social_Net{
    SumAccum<INT> @@males = 0;
    SumAccum<INT> @@females = 0;
    SumAccum<INT> @@unknown = 0;
    starting_vertex = {seed};

    people = SELECT v FROM starting_vertex -(Friend:e)-:v
        ACCUM
            CASE v.gender
                WHEN "Male" THEN @@males += 1
                WHEN "Female" THEN @@females +=1
            ELSE @@unknown += 1
        END;
	PRINT @@males, @@females, @@unknown;
}

Example 2 Results for Query count_gender_of_friends

RUN QUERY countGenderOfFriends("person4")
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{
    "@@males": 2,
    "@@unknown": 0,
    "@@females": 1
  }]
}

Query
Results

This query gives each user post a rating based on the subject and how many likes it has.

CREATE QUERY rate_posts() FOR GRAPH Social_Net API("v2") {
    SumAccum<INT> @rating = 0;
    all_people = {Person.*};

    results = SELECT v FROM all_people -(:e)- Post:v
        ACCUM CASE e.type
            WHEN "Posted" THEN
                CASE
                    WHEN v.subject == "cats" THEN v.@rating += -1
                    WHEN v.subject == "Graphs" THEN v.@rating += 2
                    WHEN v.subject == "tigergraph" THEN v.@rating += 10
                END
            WHEN "Liked" THEN v.@rating += 3 END;
    PRINT results[results.@rating];
}

Example 4 Results for Query ratePosts

GSQL > RUN QUERY rate_posts()
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"results": [
    {
      "v_id": "0",
      "attributes": {"results.@rating": 11},
      "v_type": "post"
    },
    {
      "v_id": "10",
      "attributes": {"results.@rating": 2},
      "v_type": "post"
    },
    {
      "v_id": "2",
      "attributes": {"results.@rating": 0},
      "v_type": "post"
    },
    {
      "v_id": "4",
      "attributes": {"results.@rating": 6},
      "v_type": "post"
    },
    {
      "v_id": "9",
      "attributes": {"results.@rating": -1},
      "v_type": "post"
    },
    {
      "v_id": "3",
      "attributes": {"results.@rating": 2},
      "v_type": "post"
    },
    {
      "v_id": "5",
      "attributes": {"results.@rating": 10},
      "v_type": "post"
    },
    {
      "v_id": "7",
      "attributes": {"results.@rating": 2},
      "v_type": "post"
    },
    {
      "v_id": "1",
      "attributes": {"results.@rating": 10},
      "v_type": "post"
    },
    {
      "v_id": "11",
      "attributes": {"results.@rating": -1},
      "v_type": "post"
    },
    {
      "v_id": "8",
      "attributes": {"results.@rating": 2},
      "v_type": "post"
    },
    {
      "v_id": "6",
      "attributes": {"results.@rating": 13},
      "v_type": "post"
    }
  ]}]
}

`WHILE` Statement

The WHILE statement provides unbounded iteration over a block of statements. WHILE statements can be used as query-body statements or DML-sub-statements. (See the note about differences in block syntax.)

Syntax

WHILE syntax

queryBodyWhileStmt := WHILE condition [LIMIT simpleSize] DO queryBodyStmts END
dmlSubWhileStmt :=    WHILE condition [LIMIT simpleSize] DO dmlSubStmtList END
simpleSize := integer | varName | paramName

The WHILE statement iterates over its body ( queryBodyStmts or dmlSubStmtList ) until the condition evaluates to false or until the iteration limit is met. A condition is any expression that evaluates to a boolean. The condition is evaluated before each iteration. CONTINUE statements can be used to change the control flow within the while block. BREAK statements can be used to exit the while loop.

A WHILE statement may have an optional LIMIT clause. LIMIT clauses has a constant positive integer value or integer variable to constrain the maximum number of loop iterations. The example below demonstrates how the LIMIT behaves.

If a limit value is not specified, it is possible for a WHILE loop to iterate infinitely. It is the responsibility of the query author to design the condition logic so that it is guaranteed to eventually be true (or to set a limit).

The following three WHILE statements behave the same. Each terminates when v.size == 0 or after 5 iterations of the loop.

WHILE LIMIT semantics

WHILE v.size() !=0 LIMIT 5 DO
    // Statements
END;

INT iter = 0;
WHILE (v.size() !=0) AND (iter < 5) DO
    // Statements
    iter = iter + 1;
END;

INT iter = 0;
WHILE v.size() !=0 DO
    IF iter == 5 THEN  BREAK;  END;
    // Statements
	iter = iter + 1;
END;

Examples

Below are a number of examples that demonstrate the use of WHILE statements.

Query
Results

The following query finds all vertices which are reachable from a starting seed vertex (i.e., breadth-first search)

Example 1. Simple WHILE loop

CREATE QUERY reachable(VERTEX<Person> seed) FOR GRAPH Work_Net
{
    OrAccum @visited;
    reachable_vertices = {};
    visited_vertices (ANY) = {seed};

    // Loop terminates when all neighbors are visited
    WHILE visited_vertices.size() !=0 DO
    // s is all neighbors of visited_vertices which have not been visited
        visited_vertices = SELECT s
            FROM visited_vertices-(:e)-:s
            WHERE s.@visited == FALSE
            POST-ACCUM
                s.@visited = true;
        reachable_vertices = reachable_vertices UNION visited_vertices;
    END;
    PRINT reachable_vertices;
}

RUN QUERY reachable("person1")
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"reachableVertices": [
    {
      "v_id": "person3",
      "attributes": {
        "interestList": ["teaching"],
        "skillSet": [ 6, 1, 4 ],
        "skillList": [ 4, 1, 6 ],
        "locationId": "jp",
        "interestSet": ["teaching"],
        "@visited": true,
        "id": "person3"
      },
      "v_type": "person"
    },
    {
      "v_id": "person9",
      "attributes": {
        "interestList": [ "financial", "teaching" ],
        "skillSet": [ 2, 7, 4 ],
        "skillList": [ 4, 7, 2 ],
        "locationId": "us",
        "interestSet": [ "teaching", "financial" ],
        "@visited": true,
        "id": "person9"
      },
      "v_type": "person"
    },
    {
      "v_id": "person4",
      "attributes": {
        "interestList": ["football"],
        "skillSet": [ 10, 1, 4 ],
        "skillList": [ 4, 1, 10 ],
        "locationId": "us",
        "interestSet": ["football"],
        "@visited": true,
        "id": "person4"
      },
      "v_type": "person"
    },
    {
      "v_id": "person7",
      "attributes": {
        "interestList": [ "art", "sport" ],
        "skillSet": [ 6, 8 ],
        "skillList": [ 8, 6 ],
        "locationId": "us",
        "interestSet": [ "sport", "art" ],
        "@visited": true,
        "id": "person7"
      },
      "v_type": "person"
    },
    {
      "v_id": "person1",
      "attributes": {
        "interestList": [ "management", "financial" ],
        "skillSet": [ 3, 2, 1 ],
        "skillList": [ 1, 2, 3 ],
        "locationId": "us",
        "interestSet": [ "financial", "management" ],
        "@visited": true,
        "id": "person1"
      },
      "v_type": "person"
    },
    {
      "v_id": "person5",
      "attributes": {
        "interestList": [ "sport", "financial", "engineering" ],
        "skillSet": [ 5, 2, 8 ],
        "skillList": [ 8, 2, 5 ],
        "locationId": "can",
        "interestSet": [ "engineering", "financial", "sport" ],
        "@visited": true,
        "id": "person5"
      },
      "v_type": "person"
    },
    {
      "v_id": "person6",
      "attributes": {
        "interestList": [ "music", "art" ],
        "skillSet": [ 10, 7 ],
        "skillList": [ 7, 10 ],
        "locationId": "jp",
        "interestSet": [ "art", "music" ],
        "@visited": true,
        "id": "person6"
      },
      "v_type": "person"
    },
    {
      "v_id": "person2",
      "attributes": {
        "interestList": ["engineering"],
        "skillSet": [ 6, 5, 3, 2 ],
        "skillList": [ 2, 3, 5, 6 ],
        "locationId": "chn",
        "interestSet": ["engineering"],
        "@visited": true,
        "id": "person2"
      },
      "v_type": "person"
    },
    {
      "v_id": "person8",
      "attributes": {
        "interestList": ["management"],
        "skillSet": [ 2, 5, 1 ],
        "skillList": [ 1, 5, 2 ],
        "locationId": "chn",
        "interestSet": ["management"],
        "@visited": true,
        "id": "person8"
      },
      "v_type": "person"
    },
    {
      "v_id": "company3",
      "attributes": {
        "country": "jp",
        "@visited": true,
        "id": "company3"
      },
      "v_type": "company"
    },
    {
      "v_id": "company2",
      "attributes": {
        "country": "chn",
        "@visited": true,
        "id": "company2"
      },
      "v_type": "company"
    },
    {
      "v_id": "company1",
      "attributes": {
        "country": "us",
        "@visited": true,
        "id": "company1"
      },
      "v_type": "company"
    },
    {
      "v_id": "person10",
      "attributes": {
        "interestList": [ "football", "sport" ],
        "skillSet": [3],
        "skillList": [3],
        "locationId": "us",
        "interestSet": [ "sport", "football" ],
        "@visited": true,
        "id": "person10"
      },
      "v_type": "person"
    }
  ]}]
}

Query
Results

This query finds all vertices reachable within two hops from a starting seed vertex (i.e., breadth-first search)

CREATE QUERY reachable_within_two(VERTEX<Person> seed) FOR GRAPH Work_Net
{
    OrAccum @visited;
    reachable_vertices = {};
    visited_vertices (ANY) = {seed};

    // loop terminates when all neighbors within 2-hops of the seed vertex are visited
    WHILE visited_vertices.size() !=0 LIMIT 2 DO
        //  s is all neighbors of visited_vertices which have not been visited
        visited_vertices = SELECT s
            FROM visited_vertices-(:e)-:s
            WHERE s.@visited == false
            POST-ACCUM
                s.@visited = true;
        reachable_vertices = reachable_vertices UNION visited_vertices;
    END;
    PRINT reachable_vertices;
}

RUN QUERY reachable_within_two("person1")
[
  {
    "reachable_vertices": [
      {
        "attributes": {
          "@visited": true,
          "id": "person6",
          "interest_list": [
            "music",
            "art"
          ],
          "interest_set": [
            "music",
            "art"
          ],
          "location_id": "jp",
          "skill_list": [
            7,
            10
          ],
          "skill_set": [
            7,
            10
          ]
        },
        "v_id": "person6",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "country": "chn",
          "id": "company2"
        },
        "v_id": "company2",
        "v_type": "Company"
      },
      {
        "attributes": {
          "@visited": true,
          "country": "us",
          "id": "company1"
        },
        "v_id": "company1",
        "v_type": "Company"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person10",
          "interest_list": [
            "football",
            "sport"
          ],
          "interest_set": [
            "football",
            "sport"
          ],
          "location_id": "us",
          "skill_list": [
            3
          ],
          "skill_set": [
            3
          ]
        },
        "v_id": "person10",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person4",
          "interest_list": [
            "football"
          ],
          "interest_set": [
            "football"
          ],
          "location_id": "us",
          "skill_list": [
            4,
            1,
            10
          ],
          "skill_set": [
            4,
            1,
            10
          ]
        },
        "v_id": "person4",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person3",
          "interest_list": [
            "teaching"
          ],
          "interest_set": [
            "teaching"
          ],
          "location_id": "jp",
          "skill_list": [
            4,
            1,
            6
          ],
          "skill_set": [
            4,
            1,
            6
          ]
        },
        "v_id": "person3",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person7",
          "interest_list": [
            "art",
            "sport"
          ],
          "interest_set": [
            "art",
            "sport"
          ],
          "location_id": "us",
          "skill_list": [
            8,
            6
          ],
          "skill_set": [
            8,
            6
          ]
        },
        "v_id": "person7",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person2",
          "interest_list": [
            "engineering"
          ],
          "interest_set": [
            "engineering"
          ],
          "location_id": "chn",
          "skill_list": [
            2,
            3,
            5,
            6
          ],
          "skill_set": [
            2,
            3,
            5,
            6
          ]
        },
        "v_id": "person2",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person1",
          "interest_list": [
            "management",
            "financial"
          ],
          "interest_set": [
            "management",
            "financial"
          ],
          "location_id": "us",
          "skill_list": [
            1,
            2,
            3
          ],
          "skill_set": [
            1,
            2,
            3
          ]
        },
        "v_id": "person1",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person5",
          "interest_list": [
            "sport",
            "financial",
            "engineering"
          ],
          "interest_set": [
            "sport",
            "financial",
            "engineering"
          ],
          "location_id": "can",
          "skill_list": [
            8,
            2,
            5
          ],
          "skill_set": [
            8,
            2,
            5
          ]
        },
        "v_id": "person5",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person8",
          "interest_list": [
            "management"
          ],
          "interest_set": [
            "management"
          ],
          "location_id": "chn",
          "skill_list": [
            1,
            5,
            2
          ],
          "skill_set": [
            1,
            5,
            2
          ]
        },
        "v_id": "person8",
        "v_type": "Person"
      },
      {
        "attributes": {
          "@visited": true,
          "id": "person9",
          "interest_list": [
            "financial",
            "teaching"
          ],
          "interest_set": [
            "financial",
            "teaching"
          ],
          "location_id": "us",
          "skill_list": [
            4,
            7,
            2
          ],
          "skill_set": [
            4,
            7,
            2
          ]
        },
        "v_id": "person9",
        "v_type": "Person"
      }
    ]
  }
]

`FOREACH` Statement

The FOREACH statement provides bounded iteration over a block of statements. FOREACH statements can be used as query-body statements or DML-sub-statements. See the note about differences in block syntax.

Syntax

FOREACH syntax

queryBodyForEachStmt := FOREACH forEachControl DO queryBodyStmts END
dmlSubForEachStmt :=    FOREACH forEachControl DO dmlSubStmtList END

forEachControl := ( iterationVar | "(" keyVar ("," valueVar)+ ")") (IN | ":") setBagExpr
                | iterationVar IN RANGE "[" expr "," expr"]" ["." STEP(" expr ")"]
iterationVar := name
keyVar := name
valueVar := name

The formal syntax for forEachControl appears can be broken down into the following cases:

name IN setBagExpr
(key, value) pair IN setBagExpr // because it’s a Map
name IN RANGE [ expr, expr ]
name IN RANGE [ expr, expr ].STEP ( expr )

Note that setBagExpr includes container accumulators and explicit sets.

Limitations

The FOREACH statement has the following restrictions:

In a DML-sub level FOREACH, it is never permissible to update the loop variable (the variable declared before IN, e.g., var in “FOREACH var IN setBagExpr”).
In a query-body level FOREACH, in most cases it is not permissible to update the loop variable. The following exceptions apply:
- If the iteration is over a ListAccum, its values can be updated.
- If the iteration is over a MapAccum, its values can be updated, but its keys cannot.
If the iteration is over a set of vertices, it is not permissible to access (read or write) their vertex-attached accumulators.
A query-body-level FOREACH cannot iterate over a set or bag of constants. For example, FOREACH i in (1,2,3) is not supported. However, DML-sub FOREACH does support this.

`FOREACH … IN RANGE`

The FOREACH statement has an optional RANGE clause RANGE[expr, expr], which can be used to define the iteration collection. Optionally, the range may specify a step size: RANGE[expr, expr].STEP(expr)

Each expr must evaluate to an integer. Any of the integers may be negative, but the step expr may not be 0.

The clause RANGE[a,b].STEP(c) produces the sequence of integers from a to b, inclusive, with step size c. That is, \((a, a+c, a+2*c, a+3*c, ... a+k*c)\), where k = the largest integer such that \(|k*c| ≤ |b-a|\).

If the .STEP method is not given, then the step size c = 1.

Query
Results

Nested FOREACH IN RANGE with MapAccum

CREATE QUERY foreach_range_ex() FOR GRAPH Social_Net {
    ListAccum<INT> @@t;
    Start = {Person.*};
    FOREACH i IN RANGE[0, 2] DO
        @@t += i;
        L = SELECT Start
            FROM Start
            WHERE Start.id == "person1"
            ACCUM
                FOREACH j IN RANGE[0, i] DO
                    @@t += j
                END;
    END;
    PRINT @@t;
}

Results for Query foreachRangeEx

GSQL > RUN QUERY foreach_range_ex()
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"@@t": [ 0, 0, 1, 0, 1, 2, 0, 1, 2 ]}]
}

Query
Results

The following FOREACH statement uses a specified step value for iterating through the range.

CREATE QUERY foreach_range_step(INT a, INT b, INT c) FOR GRAPH Minimal_Net {
    ListAccum<INT> @@t;
    FOREACH i IN RANGE[a,b].step(c) DO
        @@t += i;
    END;
    PRINT @@t;
}

The step value can be positive for an ascending range or negative for a descending range. If the step has the wrong polarity, then the loop has zero iterations; that is, the exit condition is already satisfied.

RUN QUERY foreach_range_step(100,0,-9)
{
  "error": false,
  "message": "",
  "version": {
    "schema": 0,
    "edition": "enterprise",
    "api": "v2"
  },
  "results": [{"@@t": [
    100,
    91,
    82,
    73,
    64,
    55,
    46,
    37,
    28,
    19,
    10,
    1
  ]}]
}

Query-body-level FOREACH Examples

Query
Results

This query counts the number of companies whose country matches the provided string.

CREATE QUERY company_count(STRING country_name) FOR GRAPH Work_Net {
    ListAccum<STRING> @@company_list;
    INT country_count;
    start = {ANY};

    // Select all vertices with type "Company", and append country attribute from all company vertices to list accum
    s = SELECT v FROM start:v
        WHERE v.type == "Company"
        ACCUM @@company_list += v.country;

    // Iterate the ListAccum and compare each element to the country_name parameter
    FOREACH item in @@company_list DO
        IF item == country_name THEN
            country_count = country_count + 1;
        END;
    END;
  PRINT country_count;
}

RUN QUERY company_count("us")
{
  "error": false,
  "message": "",
  "version": {
    "schema": 0,
    "edition": "enterprise",
    "api": "v2"
  },
  "results": [{"country_count": 2}]
}

Query
Results

This query counts the number of employees from a given country and list their IDs.

CREATE QUERY employee_by_country(STRING country_name) FOR GRAPH Work_Net {
    MapAccum <STRING, ListAccum<STRING>> @@employees;

    // Start will have a set of all person type vertices
    start = {Person.*};

    // Build a map using person location_id as a key and a list of strings to hold multiple person ids
    s = SELECT v FROM start:v
        ACCUM @@employees += (v.location_id -> v.id);

    // Iterate the map using (key,value) pairs
    FOREACH (key,val) IN @@employees DO
        IF key == country_name THEN
        PRINT val.size();

            // Nested foreach to iterate over the list of person ids
            FOREACH employee in val DO
                PRINT employee;
            END;

            // MapAccum keys are unique so we can BREAK out of the loop
            BREAK;
        END;
    END;
}

RUN QUERY employee_by_country("us")
{
  "error": false,
  "message": "",
  "version": {
    "schema": 0,
    "edition": "enterprise",
    "api": "v2"
  },
  "results": [
    {"val.size()": 5},
    {"employee": "person7"},
    {"employee": "person1"},
    {"employee": "person4"},
    {"employee": "person9"},
    {"employee": "person10"}
  ]
}

DML-sub FOREACH Examples

Query
Results

This query shows post topics liked by users and show total likes per topic.

CREATE QUERY topic_likes() FOR GRAPH Social_Net {
    SetAccum<STRING> @@person_osts;
    SumAccum<INT> @post_likes;
    MapAccum<STRING,INT> @@likes_by_topic;

    start = {Person.*};

    // Find all user posts and generate a set of post topics
    // (set has no duplicates)
    posts = SELECT g FROM start - (Posted>) - :g
          ACCUM @@person_posts += g.subject;

    // Use set of topics to increment how many times a specific
    // post is liked by other users
    liked_posts = SELECT f FROM start - (Liked>) - :f
        ACCUM FOREACH x in @@person_posts DO
        CASE WHEN (f.subject == x) THEN
            f.@post_likes += 1
            END
        END
    // Aggregate all liked totals by topic
    POST-ACCUM @@likes_by_topic += (f.subject -> f.@post_likes);

    // Display the number of likes per topic
    PRINT @@likes_by_topic;
}

GSQL > RUN QUERY topic_likes()
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"@@likesByTopic": {
    "cats": 3,
    "coffee": 2,
    "Graphs": 3,
    "tigergraph": 1
  }}]
}

Query
Results

This query shows a summary of the number of friends all persons have by gender.

CREATE QUERY friend_gender() FOR GRAPH Social_Net {
    ListAccum<STRING> @friend_gender;
    SumAccum<INT> @@male_gender_count;
    SumAccum<INT> @@female_gender_count;

    start = {Person.*};

    // Record a list showing each friend's gender
    social_members = SELECT s FROM start:s -(Friend)- :g
        ACCUM s.@friend_gender += (g.gender)
    // Loop over each list of genders and total them
        POST-ACCUM
            FOREACH a in s.@friend_gender DO
                CASE WHEN (a == "Male") THEN
                    @@male_gender_count += 1
                ELSE
                    @@female_gender_count += 1
                END
            END;

    PRINT @@male_gender_count;
    PRINT @@female_gender_count;
}

GSQL > RUN QUERY friend_gender()
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [
    {"@@maleGenderCount": 11},
    {"@@femaleGenderCount": 7}
  ]
}

`CONTINUE` and `BREAK` Statements

The CONTINUE and BREAK statements can only be used within a block of a WHILE or FOREACH statement. The CONTINUE statement branches control flow to the end of the loop, skipping any remaining statements in the current iteration, and proceeding to the next iteration. That is, everything in the loop block after the CONTINUE statement will be skipped, and then the loop will continue as normal.

The BREAK statement branches control flow out of the loop, i.e., it will exit the loop and stop iteration.

Examples

Below are a number of examples that demonstrate the use of BREAK and CONTINUE.

Continue and Break Semantics

// While loop with continue statement
    INT i = 0;
    INT nCount = 0;
    WHILE i < 10 DO
        i = i + 1;
        IF (i % 2 == 0) { CONTINUE; }
        nCount = nCount + 1;
    END;
    // i is 10, nCount is 5 (skips the increment for every even i).

    // While loop with a break statement
    i = 0;
    WHILE i < 10 DO
        IF (i == 5) { BREAK; }  # When i is 5 the loop is exited
        i = i + 1;
    END;
// i is now 5

Query
Results

This query finds posts of a given person, and post of friends of that person, friends of friends, etc. until a post about cats is found. The number of friend-hops to reach is the 'degree' of cats.

CREATE QUERY find_degree_of_cats(VERTEX<Person> seed) FOR GRAPH Social_Net
{
    SumAccum<INT> @@degree = 0;
    OrAccum @@found_cat_post = FALSE;
    OrAccum @visited = FALSE;

    friends (ANY) = {seed};
    WHILE @@found_cat_post != true AND friends.size() > 0 DO
        posts = SELECT v FROM friends-(Posted>:e)-:v
            ACCUM CASE WHEN v.subject == "cats" THEN
                @@found_cat_post += true
            END;

        IF @@found_cat_post THEN
            BREAK;
        END;

        friends = SELECT v FROM friends-(Friend:e)-:v
            WHERE v.@visited == false
            ACCUM v.@visited = true;

        @@degree += 1;
    END;
    PRINT @@degree;

}

RUN QUERY find_degree_of_cats("person2")
{
  "error": false,
  "message": "",
  "version": {
    "schema": 0,
    "edition": "enterprise",
    "api": "v2"
  },
  "results": [{"@@degree": 2}]
}

Query
Results

This query finds all 3-hop friends of a starting vertex. Count coworkers as friends if there are not enough friends

CREATE QUERY find_enough_friends(VERTEX<Person> seed) FOR GRAPH Friend_Net
{
    // Keep track of the distance from the seed
    SumAccum<INT> @@distance = 0;
    OrAccum @visited = false;
    visited_vertices = {seed};
    WHILE true LIMIT 3 DO
        @@distance += 1;
        // Traverse from visited_vertices to its friends
        friends = SELECT v
            FROM visited_vertices -(Friend:e)- :v
            WHERE v.@visited == false
            POST-ACCUM v.@visited = true;
        PRINT @@distance, friends;

        // If number of friends at this level is sufficient, finish this iteration
        IF visited_vertices.size() >= 2 THEN
            visited_vertices = friends;
            CONTINUE;
        END;
        // If fewer than 4 friends, add in coworkers
        coworkers = SELECT v
            FROM visited_vertices -(Coworker:e)- :v
            WHERE v.@visited == false
            POST-ACCUM v.@visited = true;
        visited_vertices = friends UNION coworkers;
        PRINT @@distance, coworkers;
    END;
}

findEnoughFriends.json Example 2 Results

RUN QUERY find_enough_friends("person1")
{
  "error": false,
  "message": "",
  "version": {
    "schema": 0,
    "edition": "enterprise",
    "api": "v2"
  },
  "results": [
    {
      "@@distance": 1,
      "friends": [
        {
          "v_id": "person4",
          "attributes": {
            "@visited": true,
            "id": "person4"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person2",
          "attributes": {
            "@visited": true,
            "id": "person2"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person3",
          "attributes": {
            "@visited": true,
            "id": "person3"
          },
          "v_type": "Person"
        }
      ]
    },
    {
      "coworkers": [
        {
          "v_id": "person5",
          "attributes": {
            "@visited": true,
            "id": "person5"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person6",
          "attributes": {
            "@visited": true,
            "id": "person6"
          },
          "v_type": "Person"
        }
      ],
      "@@distance": 1
    },
    {
      "@@distance": 2,
      "friends": [
        {
          "v_id": "person1",
          "attributes": {
            "@visited": true,
            "id": "person1"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person8",
          "attributes": {
            "@visited": true,
            "id": "person8"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person9",
          "attributes": {
            "@visited": true,
            "id": "person9"
          },
          "v_type": "Person"
        }
      ]
    },
    {
      "@@distance": 3,
      "friends": [
        {
          "v_id": "person7",
          "attributes": {
            "@visited": true,
            "id": "person7"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person10",
          "attributes": {
            "@visited": true,
            "id": "person10"
          },
          "v_type": "Person"
        },
        {
          "v_id": "person12",
          "attributes": {
            "@visited": true,
            "id": "person12"
          },
          "v_type": "Person"
        }
      ]
    }
  ]
}

Control Flow Statements

Differences in Block Syntax

IF Statement

Syntax

Examples

CASE Statement

Syntax

Examples

WHILE Statement

Syntax

Examples

FOREACH Statement

Syntax

Limitations

FOREACH …​ IN RANGE

Query-body-level FOREACH Examples

DML-sub FOREACH Examples

CONTINUE and BREAK Statements

Examples

`IF` Statement

`CASE` Statement

`WHILE` Statement

`FOREACH` Statement

`FOREACH … IN RANGE`

`CONTINUE` and `BREAK` Statements