Function sum() sums up a column of numbers, or concatenates a column of string. Only one row from the data stream will be kept after this function is called, and all the rest rows will be abandoned.

Arguments：

• Number or string <number | string>, auto-abstraction: UUID of NODE/EDGE, row index (starting from 0) of PATH/TABLE, or the first element of ARRAY

Returns：

• Sum or new string <number | string>

ATTR (Numeric value)

Example: find the outbound 1-step transfer paths from Card CA001, return the sum of the transfer amounts

n({_id == "CA001"}).re({@transfer} as pay).n({@card})
return sum(pay.amount)

ATTR (String)

Example: find the outbound 1-step transfer paths from Card CA001, return the strings converted from payee cards' IDs

n({_id == "CA001"}).re({@transfer}).n({@card} as payee)
return sum(payee._id)