Issue found on page 'Set Operations'

[dmcmurchy]

Page URL: https://duckdb.org/docs/sql/query_syntax/setops#union

The documentation under UNION states:

The UNION clause can be used to combine rows from multiple queries. The queries are required to have the same number of columns and the same column types.

• This seems to imply that if the column types are not the same an error would occur as DuckDB does error on a difference in the number of columns.

Under the Set Operations it states: If the columns are not of the same type, casts may be added.

• Which is happening in my example below, but the UNION documentation that followed seems to counteract this statement.

Example: When replicating a PostgreSQL query, if I have one column as VARCHAR and one column as BIGINT and I perform a UNION of these columns using DuckDB the resulting output type is a VARCHAR, with PostgreSQL this generates an error.

Originally, I thought this was possibly a bug, but found the following discussion which is apparently the intended behaviour.

I believe the documentation should be updated to reflect that an implicit cast could occur if the column types are not the same under the UNION heading.

I wasn't able to find a way to get the same behaviour as PostgreSQL and if there is a way it would be nice if this could be documented.