I have an Excel file with year column as 2017, 2016, 2015 etc. In addition I have a month colmun. When I source this Excel sheet, the year as oppose to the month column is not recognized by PowerBI as a date but an integer which can be summarized (under modeling tab the “Data Type” for the year column appears as a “Whole Number”).
When I’m trying to re-format this column into a date format it throws an error stating “We can’t automatically convert the column to Date type”. So I went and add a new column sourcing my year column and tried to reformat the new one.
Apparently this worked to some extent as all years got converted to 1905.
In Power BI, it’s impossible to set a year column to 'Date' type in “yyyy” format. If you change a column with just years into date type format, it will format your data into a date.
Why does it do this? Well, it's probably because there is really no reason to convert years to a Date field anyway. It doesn't give you any extra functionality or anything. You can use the year field however you want (as a filter, in a visual, in a measure) WITHOUT it being in Date format!
My suggestion: leave the column in whole number / integer format.