[GitHub] [arrow] Dandandan commented on a change in pull request #9866: ARROW-12109: [Rust][DataFusion] Implement SHOW COLUMNS

[GitBox <gi...@apache.org>]

Dandandan commented on a change in pull request #9866:
URL: https://github.com/apache/arrow/pull/9866#discussion_r605964671



##########
File path: rust/datafusion/src/sql/planner.rs
##########
@@ -1305,6 +1304,74 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
             )))
         }
     }
+
+    fn show_columns_to_plan(
+        &self,
+        extended: bool,
+        full: bool,
+        table_name: &ObjectName,
+        filter: Option<&ShowStatementFilter>,
+    ) -> Result<LogicalPlan> {
+        if filter.is_some() {
+            return Err(DataFusionError::Plan(
+                "SHOW COLUMNS with WHERE or LIKE is not supported".to_string(),
+            ));
+        }
+
+        if !self.has_table("information_schema", "columns") {
+            return Err(DataFusionError::Plan(
+                "SHOW COLUMNS is not supported unless information_schema is enabled"
+                    .to_string(),
+            ));
+        }
+
+        if self
+            .schema_provider
+            .get_table_provider(table_name.try_into()?)
+            .is_none()
+        {
+            return Err(DataFusionError::Plan(format!(
+                "Unknown relation for SHOW COLUMNS: {}",
+                table_name
+            )));
+        }
+
+        // Figure out the where clause
+        let columns = vec!["table_name", "table_schema", "table_catalog"].into_iter();
+        let where_clause = table_name
+            .0
+            .iter()
+            .rev()

Review comment:
       Why `rev` and not listing the items in column in reverse?




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