geoffreyclaude commented on code in PR #130:
URL: https://github.com/apache/datafusion-site/pull/130#discussion_r2661730358
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content/blog/2025-12-18-extending-sql.md:
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+---
+layout: post
+title: Extending SQL in DataFusion: from ->> to TABLESAMPLE
+date: 2025-12-18
+author: Geoffrey Claude (Datadog)
+categories: [tutorial]
+---
+
+<!--
+{% comment %}
+Licensed to the Apache Software Foundation (ASF) under one or more
+contributor license agreements. See the NOTICE file distributed with
+this work for additional information regarding copyright ownership.
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+(the "License"); you may not use this file except in compliance with
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+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+{% endcomment %}
+-->
+
+[TOC]
+
+## When standard SQL isn't enough
+
+If you embed [DataFusion][apache datafusion] in your product, your users will
eventually run SQL that DataFusion does not recognize. Not because the query is
unreasonable, but because SQL in practice includes many dialects and
system-specific statements.
+
+Suppose you store data as Parquet files on S3 and want users to attach an
external catalog to query them. DataFusion has `CREATE EXTERNAL TABLE` for
individual tables, but no built-in equivalent for catalogs. DuckDB has
`ATTACH`, SQLite has its own variant, but what you really want is something
more flexible:
+
+```sql
+CREATE EXTERNAL CATALOG my_lake
+STORED AS iceberg
+LOCATION 's3://my-bucket/warehouse'
+OPTIONS ('region' 'eu-west-1');
+```
+
+This syntax does not exist in DataFusion today, but you can add it.
+
+---
+
+At the same time, many dialect gaps are smaller and show up in everyday
queries:
+
+```sql
+-- Postgres-style JSON operators
+SELECT payload->'user'->>'id' FROM logs;
+
+-- MySQL-specific types
+SELECT DATETIME '2001-01-01 18:00:00';
+
+-- Statistical sampling
+SELECT * FROM sensor_data TABLESAMPLE BERNOULLI(10 PERCENT);
+```
+
+You can implement all of these _without forking_ DataFusion:
+
+1. **Parse** new syntax (custom statements / dialect quirks)
+2. **Plan** new semantics (expressions, types, FROM-clause constructs)
+3. **Execute** new operators when rewrites are not sufficient
+
+This post explains where and how to hook into each stage. For complete,
working code, see the linked `datafusion-examples`.
+
+---
+
+## Parse → Plan → Execute
+
+DataFusion turns SQL into executable work in stages:
+
+1. **Parse**: SQL text is parsed into an AST (`Statement` from [sqlparser-rs])
+2. **Logical planning**: `SqlToRel` converts the AST into a `LogicalPlan`
+3. **Physical planning**: The `PhysicalPlanner` turns the logical plan into an
`ExecutionPlan`
+
+Each stage has extension points.
+
+<figure>
Review Comment:
And you should see the static webpage I vibe-coded to tune the svg 😆
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