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There are some operators that have more than one output. Each output is provided via a port. The default port is 0, the second one is 1 etc. The selection for example, pushes all elements that fulfill the predicate to output port 0 and all other to output port 1. So, if you want to use another port, you can prepend the port number with a colon in front of the operator. For example, if you want the second output (port 1) of the select:

PROJECT({…}, 1:SELECT({predicate=RelationalPredicate('1<x')}, …))

The Full Grammar of PQL

QUERY           = (TEMPORARYSTREAM | VIEW | SHAREDSTREAM)+
TEMPORARYSTREAM = STREAM "=" OPERATOR
VIEW            = VIEWNAME ":=" OPERATOR
SHAREDSTREAM    = SOURCENAME "::=" OPERATOR
OPERATOR        = QUERY | [OUTPUTPORT ":"] OPERATORTYPE "(" (PARAMETERLIST [ "," OPERATORLIST ] | OPERATORLIST) ")"
OPERATORLIST    = [ OPERATOR ("," OPERATOR)* ]
PARAMETERLIST   = "{" PARAMETER ("," PARAMETER)* "}"
PARAMETER       = NAME "=" PARAMETERVALUE
PARAMETERVALUE  = LONG | DOUBLE | STRING | PREDICATE | LIST | MAP
LIST            = "[" [PARAMETERVALUE ("," PARAMETERVALUE)*] "]"
MAP             = "[" [MAPENTRY ("," MAPENTRY*] "]"
MAPENTRY        = PARAMETERVALUE "=" PARAMETERVALUE
STRING          = "'" [~']* "'"
PREDICATE       = PREDICATETYPE "(" STRING ")"

List of available PQL Operators

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