Update comments to clarify the unsupported status of UPDATE ... FROM syntax

Author: kosiew

datafusion/core/tests/custom_sources_cases/dml_planning.rs

@@ -725,8 +725,8 @@ async fn test_delete_target_table_scoping() -> Result<()> {
 
 #[tokio::test]
 async fn test_update_from_drops_non_target_predicates() -> Result<()> {
-    // UPDATE ... FROM is currently unsupported due to design limitations
-    // See FIX_UPDATE.md and FIX_UPDATE_2.md for details
+    // UPDATE ... FROM is currently not working
+    // TODO fix https://github.com/apache/datafusion/issues/19950
     let target_provider = Arc::new(CaptureUpdateProvider::new_with_filter_pushdown(
         test_schema(),
         TableProviderFilterPushDown::Exact,

datafusion/sql/src/statement.rs

@@ -1071,9 +1071,8 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
                 }
                 let update_from = from_clauses.and_then(|mut f| f.pop());
 
-                // UPDATE ... FROM is currently unsupported due to design limitations
-                // See FIX_UPDATE.md and FIX_UPDATE_2.md for details
-                // Qualifier stripping breaks source column references, causing incorrect behavior
+                // UPDATE ... FROM is currently not working
+                // TODO fix https://github.com/apache/datafusion/issues/19950
                 if update_from.is_some() {
                     return not_impl_err!("UPDATE ... FROM is not supported");
                 }

datafusion/sqllogictest/test_files/update.slt

@@ -80,7 +80,7 @@ insert into t2 values (1, 'updated_b', 5.0, 40), (2, 'updated_b2', 2.5, 50), (4,
 
 # UPDATE ... FROM is currently unsupported - qualifier stripping breaks source column references
 # causing assignments like 'b = t2.b' to resolve to target table's 'b' instead of source table's 'b'
-# See FIX_UPDATE.md and FIX_UPDATE_2.md for details
+# TODO fix https://github.com/apache/datafusion/issues/19950
 statement error DataFusion error: This feature is not implemented: UPDATE ... FROM is not supported
 update t1 set b = t2.b, c = t2.a, d = 1 from t2 where t1.a = t2.a and t1.b > 'foo' and t2.c > 1.0;
 
@@ -90,6 +90,7 @@ explain update t1 set b = t2.b, c = t3.a, d = 1 from t2, t3 where t1.a = t2.a an
 
 # test table alias
 # UPDATE ... FROM is currently unsupported
+# TODO fix https://github.com/apache/datafusion/issues/19950
 query error DataFusion error: This feature is not implemented: UPDATE ... FROM is not supported
 explain update t1 as T set b = t2.b, c = t.a, d = 1 from t2 where t.a = t2.a and t.b > 'foo' and t2.c > 1.0;
 
@@ -107,5 +108,6 @@ statement ok
 insert into t2 values (1, 'new_val', 2.0, 100), (2, 'new_val2', 1.5, 200);
 
 # UPDATE ... FROM is currently unsupported
+# TODO fix https://github.com/apache/datafusion/issues/19950
 statement error DataFusion error: This feature is not implemented: UPDATE ... FROM is not supported
 update t1 as T set b = t2.b, c = t.a, d = 1 from t2 where t.a = t2.a and t.b > 'foo' and t2.c > 1.0;