Compatible data types in set operations

Question

Accepted Answer

Set operations match columns by position: the first column of each SELECT is combined, the second column of each SELECT is combined, and so on. Here, order_date (a date type) is paired with price (a decimal), which are incompatible - the database cannot determine what type the result column should be. Column names do not need to match; only the number of columns and their positional type compatibility matter.