kosiew commented on code in PR #19221:
URL: https://github.com/apache/datafusion/pull/19221#discussion_r2629630912
##########
datafusion/sql/src/unparser/dialect.rs:
##########
@@ -218,6 +218,46 @@ pub trait Dialect: Send + Sync {
fn timestamp_with_tz_to_string(&self, dt: DateTime<Tz>, _unit: TimeUnit)
-> String {
dt.to_string()
}
+
+ /// Whether the dialect supports an empty select list such as `SELECT FROM
table`.
+ ///
+ /// An empty select list returns rows without any column data, which is
useful for:
+ /// - Counting rows: `SELECT FROM users WHERE active = true` (combined
with `COUNT(*)`)
+ /// - Testing row existence without retrieving column data
+ /// - Performance optimization when only row counts or existence checks
are needed
+ ///
+ /// # Supported Databases
+ ///
+ /// - **PostgreSQL**: Fully supported. Returns rows with zero columns.
+ /// - **DataFusion**: Supported natively.
Review Comment:
I'll remove it.
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