I need to convert column type from decimal to date in sparksql when the format is not yyyy-mm-dd?

A table contains column data declared as decimal (38,0) and data is in yyyymmdd format and I am unable to run sql queries on it in databrick notebook.

I have tried to_date(column_name) = date_sub(current_date(),1) and it didn't work. I tried, "from_unixtime(cast(column_name as string), 'yyyy-MM-dd') or to_date(cast(unix_timestamp('column_name, 'yyyy-MM-dd') and none of them are work. From_unixtime(cast(column_name as string),'yyyy-mm-dd', it gives me right format but those data are not existed in the table.

How can I convert this column type to a date inside sql?