`except': EXCEPT not supported (Sequel::InvalidOperation)

i have encountered an error while trying run an sinatra application. I
tried googling it and nothing came up. If you guys can offer any advice
on how to fix it or what i am doing wrong it will be great help.

Part of the Code that is erroring out

def logTownDeltas!(newDate)
deltas = []

    oldTowns = @db[:towns].filter { data_timestamp < newDate }
    currentTowns = @db[:towns].except(oldTowns)

    destroyedTownIDs =

oldTowns.select(:town_id).except(currentTowns.select(:town_id)).collect
{ |d| d[:town_id] }
createdTownIDs =
currentTowns.select(:town_id).except(oldTowns.select(:town_id)).collect
{ |c| c[:town_id] }

    alteredTowns = Hash.new
    currentTowns.each { |town|

    }

ERROR

C:/Ruby22/lib/ruby/gems/2.2.0/gems/sequel-4.29.0/lib/sequel/dataset/query.rb:119:in

except': EXCEPT not supported (Sequel::InvalidOperation) from C:/Users/dakota/Desktop/IllyriadAp/data_syndicator/core.rb:107:inlogTownDeltas!’
from
C:/Users/dakota/Desktop/IllyriadAp/data_syndicator/core.rb:93:in
parseTownData' from C:/Users/dakota/Desktop/IllyriadAp/data_syndicator/core.rb:45:inblock
(2 levels) in run!’
from C:/Ruby22/lib/ruby/2.2.0/open-uri.rb:154:in open_uri' from C:/Ruby22/lib/ruby/2.2.0/open-uri.rb:716:inopen’
from C:/Ruby22/lib/ruby/2.2.0/open-uri.rb:34:in open' from C:/Users/dakota/Desktop/IllyriadAp/data_syndicator/core.rb:44:inblock
in run!’
from
C:/Users/dakota/Desktop/IllyriadAp/data_syndicator/core.rb:41:in each' from C:/Users/dakota/Desktop/IllyriadAp/data_syndicator/core.rb:41:inrun!’
from data_syndicator.rb:17:in `’

https://github.com/kodabear4511/IllyriadAp/blob/master/data_syndicator/core.rb

No real idea what the problem is here but the error seems to happen in
sequel. Are you able to change the code to avoid this error?

Sequel::InvalidOperation

Whatever this in particular means, Sequel does not seem to like the
operation you are doing before. Perhaps you can sanitize the information
you have there before delegating into Sequel.

MySql doesn’t support EXCEPT syntax.

def logTownDeltas!(newDate)
deltas = []
currentTowns = @db[:towns].filter { data_timestamp >= newDate }

destroyedTownIDs = @db[:towns].select(:town_id).filter {
data_timestamp < newDate }.collect { |d| d[:town_id] }
createdTownIDs = @db[:towns].select(:town_id).filter { data_timestamp

= newDate }.collect { |c| c[:town_id] }

    alteredTowns = Hash.new
    currentTowns.each { |town|

    }

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