Thanks! Im sorry but I didn't explain it good enough. I've got one table with the historie of all city's. Like this: City Start_Year End_Year New_City New_Start New_End A 2001 2003 B 2004 2006 B 2004 2006 C 2007 2010 C 2007 2010 D 2011 2016 D 2011 2016 E 2010 2018 F 2007 2009 E 2010 2018 G 1900 2018 ... In other tables there might be incorrect data. For example information about the city A in 2008. But in 2008 the city is not A anymore but C. This is what i want to correct. So if you got a row: City Year ... ... A 2008 ... ... I want to add a variable City_correct like this, to correct the wrong city's: City Year City_correct ... ... A 2008 C ... ... Hope this is a better explanation..
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