pepijnve commented on code in PR #25112:
URL: https://github.com/apache/datafusion/pull/25112#discussion_r4070274878


##########
datafusion-examples/examples/sql_ops/custom_sql_parser.rs:
##########
@@ -16,11 +16,16 @@
 // under the License.
 
 //! This example demonstrates extending the DataFusion SQL parser to support
-//! custom DDL statements, specifically `CREATE EXTERNAL CATALOG`.
+//! custom DDL statements, specifically `CREATE FOREIGN CATALOG`.
+//!
+//! Note: DataFusion supports `CREATE EXTERNAL CATALOG` out-of-the-box making 
use of
+//! [`CatalogProviderFactory`](datafusion::catalog::CatalogProviderFactory). 
This example
+//! is a partial reimplementation of the existing functionality to demonstrate 
how to extend the
+//! SQL parser.

Review Comment:
   TBH I wasn't sure how to describe this well. The point I was trying to get 
across is that this example is only a partial reimplementation of the 
functionality provided by the built-in 'external' support. There's no 
delegation to the registered factories in `handle_create_foreign_catalog`, it's 
a simple hardcoded example only.
   
   I think it would actually be better to replace this example with something 
else that doesn't overlap with built-in functionality, but I took the easy way 
out for myself mainly due to lack of inspiration for a different (but still 
simple to implement) custom syntax alternative.



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