V4.1 

Format, Parameters

CALL executes subquery in a UQL statment. This subquery starts with WITH and ends with RETURN, and it applys query and calculation to each row of the input data stream separately, other than query all the input rows and then calculate all the results combinedly. Subquery helps caluses such as GROUP BY, ORDER BY, LIMIT, SKIP, and aggretation funtions and distinct() when processing the results of a single execution of a query statement in the UQL.

Syntax:

• Format:
  call {
    with <columnA1>, <columnA2>, ...
    ...
    return <columnB1>, <columnB2>, ...
  }
• Parameters: see table below
• Affected columns: <columnA> and all its homologous columns; when aliases are non-homologous columns, they will be trimmed to the shortest lengths to become homologous columns before calculation

Analysis

find().nodes([1, 5]) as nodes
call {
  with nodes
  n(nodes).e()[:2].n() as p
  limit 2
  return p as path
}
return path

In the UQL statement above, CALL splices data columns from a major query statement into multiple sub queries and sets row number limits to each sub query's result respectively

Single Query in Subquery

Example: do not use GROUP BY, find how many cards Customer CU001, CU002, and CU003 hold respectively

uncollect ["CU001", "CU002", "CU003"] as user
call { 
  with user
  n({_id == user}).e({@has}).n({@card} as n)
  return count(n) as number
}
return user, number

Analysis: CALL aggregates each user's n to get number, i.e. group all users n based on user and aggregate all users n in group.

Multiple Queries in Subquery

Example: find 10 transfer edges with an amount higher than 8,000 and rate each edge: if there is transfer between its end-node and bank card CA029 within 2 steps, then add 0.5 for that end-node; the sum of ratings of both end-nodes is the final rating of the edge

n({@card} as n1).re({@transfer.amount > 8000} as e).n({@card} as n2).limit(10)
call {
  with n1, n2
  optional n(n1 as a1).e({@transfer})[:2].n({_id == "CA029"}).limit(1) 
  with CASE a1 when 0 then 0 else 0.5 END as c1
  optional n(n2 as a2).e({@transfer})[:2].n({_id == "CA029"}).limit(1) 
  with CASE a2 when 0 then 0 else 0.5 END as c2
  return c1+c2 as c
}
return e{*}, c

Analysis: n1 and n2 are the startting-node and ending-node of edge e, CALL calculates ratings c1 and c2 for n1 and n2 in each row, and sum them as the total rating c for each e; the length of c is the same as the length of n1, n2 and c.