UDA examples

Calculate an average for a double precision value. This UDA performs the same function as the SQL AVG aggregate, but only for the DOUBLE data type.

SUM=1

COUNT=2

function initState(state)
state[SUM] = 0
state[COUNT] = 0
return state

end

function accumulate(state, value)
state[SUM]	= state[SUM] + value
state[COUNT] = state[COUNT] + 1
return state

end

function merge(state1, state2)
state1[SUM] = state1[SUM] + state2[SUM] state1[COUNT] = state1[COUNT] + state2[COUNT] return state1
end

function finalResult(state)
return state[SUM] / state[COUNT]

end

function getState()
state = {}
state[1] = { "sum", double }
state[2] = { "count", double }
return state
end

function getType()
return "uda"
end

function getName()
return "lua_avg"
end

function getArgs()
args = {}
args[1] = { "value", double }
return args
end

function getResult()
return double
end

The second UDA example is an analytic UDA (a UDA that is invoked with an OVER clause). This UDA can be used to create unique session identifiers for weblog data based on a session timeout value.

--[[---------------------------------------------------------

Example usage in SQL:

select
customer,
click_time,
sessionize(click_time, 900) over (partition by customer order by click_time)

from

weblog_data

--]]---------------------------------------------------------

function initState(state)
state[1] = 0
state[2] = 0
return state

end

function accumulate(state, ts, seconds)
if ts - state[1] > seconds then
state[2] = getNextId()
end
state[1] = ts
return state

end

function finalResult(state)
return state[2]

end

function getName()
return "sessionize"

end

function getType()
return "uda"

end

function getState()
state={}
state[1] = { "", timestamp }
state[2] = { "", integer	}
return state
end

function getArgs()
args={}
args[1] = { "click_time", timestamp }
args[2] = { "timeout",	integer	}
return args

end

function getResult()
return integer

end

function getOptions()
options={}
options[OPT_AGGTYPE] = "analytic"
return options

end