Perform calculation without having to do it manually for each column?

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Answer

if you want someone to provide you with a complete solution then you will need to supply:

1. CREATE TABLE statements for the 3 tables
2. INSERT INTO… statements to provide sample data for all 3 tables

However, if you just want a suggestion about how to approach this problem then I would use an UNPIVOT statement to create a view/table that

• holds all the columns in dbo.T_BASE_GEMEINDE_BEVOELKERUNG_JAHR_BEGINN
  apart from the “year” columns (J2017, J2018, j2019, …)
• adds a single “year” column with values from 2017 to 2050
• adds a single value column to hold the population for each year

By joining your existing tables to this new table/view and grouping by your new “year” column you should achieve what you want