Docs: add additional links to blog posts (#19833)

## Which issue does this PR close?

- Part of #7013 

## Rationale for this change

We have written some good blogs recently that provide additional context
and backstory. Let's make sure they are available for others to read

## What changes are included in this PR?

Add links to select doc pages
## Are these changes tested?

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## Are there any user-facing changes?

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Author: alamb

docs/source/library-user-guide/extending-sql.md

@@ -27,6 +27,11 @@ need to:
 - Add custom data types not natively supported
 - Implement SQL constructs like `TABLESAMPLE`, `PIVOT`/`UNPIVOT`, or `MATCH_RECOGNIZE`
 
+You can read more about this topic in the [Extending SQL in DataFusion: from ->>
+to TABLESAMPLE] blog.
+
+[extending sql in datafusion: from ->> to tablesample]: https://datafusion.apache.org/blog/2026/01/12/extending-sql
+
 ## Architecture Overview
 
 When DataFusion processes a SQL query, it goes through these stages:

docs/source/library-user-guide/functions/adding-udfs.md

@@ -684,6 +684,10 @@ No function matches the given name and argument types substr(Utf8).
 Scalar UDFs are functions that take a row of data and return a single value. Window UDFs are similar, but they also have
 access to the rows around them. Access to the proximal rows is helpful, but adds some complexity to the implementation.
 
+For background and other considerations, see the [User defined Window Functions in DataFusion] blog.
+
+[user defined window functions in datafusion]: https://datafusion.apache.org/blog/2025/04/19/user-defined-window-functions
+
 For example, we will declare a user defined window function that computes a moving average.
 
 ```rust

docs/source/library-user-guide/query-optimizer.md

@@ -28,8 +28,17 @@ This crate is a submodule of DataFusion that provides a query optimizer for logi
 contains an extensive set of [`OptimizerRule`]s and [`PhysicalOptimizerRule`]s that may rewrite the plan and/or its expressions so
 they execute more quickly while still computing the same result.
 
+For a deeper background on optimizer architecture and rule types and predicates, see
+[Optimizing SQL (and DataFrames) in DataFusion, Part 1], [Part 2],
+[Using Ordering for Better Plans in Apache DataFusion], and
+[Dynamic Filters: Passing Information Between Operators During Execution for 25x Faster Queries].
+
 [`optimizerrule`]: https://docs.rs/datafusion/latest/datafusion/optimizer/trait.OptimizerRule.html
 [`physicaloptimizerrule`]: https://docs.rs/datafusion/latest/datafusion/physical_optimizer/trait.PhysicalOptimizerRule.html
+[optimizing sql (and dataframes) in datafusion, part 1]: https://datafusion.apache.org/blog/2025/06/15/optimizing-sql-dataframes-part-one
+[part 2]: https://datafusion.apache.org/blog/2025/06/15/optimizing-sql-dataframes-part-two
+[using ordering for better plans in apache datafusion]: https://datafusion.apache.org/blog/2025/03/11/ordering-analysis
+[dynamic filters: passing information between operators during execution for 25x faster queries]: https://datafusion.apache.org/blog/2025/09/10/dynamic-filters
 [`logicalplan`]: https://docs.rs/datafusion/latest/datafusion/logical_expr/enum.LogicalPlan.html
 
 ## Running the Optimizer

docs/source/user-guide/concepts-readings-events.md

@@ -37,6 +37,34 @@
 
 This is a list of DataFusion related blog posts, articles, and other resources. Please open a PR to add any new resources you create or find
 
+- **2026-01-12** [Blog: Extending SQL in DataFusion: from ->> to TABLESAMPLE](https://datafusion.apache.org/blog/2026/01/12/extending-sql)
+
+- **2025-12-15** [Blog: Optimizing Repartitions in DataFusion: How I Went From Database Noob to Core Contribution](https://datafusion.apache.org/blog/2025/12/15/avoid-consecutive-repartitions)
+
+- **2025-09-21** [Blog: Implementing User Defined Types and Custom Metadata in DataFusion](https://datafusion.apache.org/blog/2025/09/21/custom-types-using-metadata)
+
+- **2025-09-10** [Blog: Dynamic Filters: Passing Information Between Operators During Execution for 25x Faster Queries](https://datafusion.apache.org/blog/2025/09/10/dynamic-filters)
+
+- **2025-08-15** [Blog: Using External Indexes, Metadata Stores, Catalogs and Caches to Accelerate Queries on Apache Parquet](https://datafusion.apache.org/blog/2025/08/15/external-parquet-indexes)
+
+- **2025-07-14** [Blog: Embedding User-Defined Indexes in Apache Parquet Files](https://datafusion.apache.org/blog/2025/07/14/user-defined-parquet-indexes)
+
+- **2025-06-30** [Blog: Using Rust async for Query Execution and Cancelling Long-Running Queries](https://datafusion.apache.org/blog/2025/06/30/cancellation)
+
+- **2025-06-15** [Blog: Optimizing SQL (and DataFrames) in DataFusion, Part 1: Query Optimization Overview](https://datafusion.apache.org/blog/2025/06/15/optimizing-sql-dataframes-part-one)
+
+- **2025-06-15** [Blog: Optimizing SQL (and DataFrames) in DataFusion, Part 2: Optimizers in Apache DataFusion](https://datafusion.apache.org/blog/2025/06/15/optimizing-sql-dataframes-part-two)
+
+- **2025-04-19** [Blog: User defined Window Functions in DataFusion](https://datafusion.apache.org/blog/2025/04/19/user-defined-window-functions)
+
+- **2025-04-10** [Blog: tpchgen-rs World's fastest open source TPC-H data generator, written in Rust](https://datafusion.apache.org/blog/2025/04/10/fastest-tpch-generator)
+
+- **2025-03-11** [Blog: Using Ordering for Better Plans in Apache DataFusion](https://datafusion.apache.org/blog/2025/03/11/ordering-analysis)
+
+- **2024-05-07** [Blog: Announcing Apache Arrow DataFusion is now Apache DataFusion](https://datafusion.apache.org/blog/2024/05/07/datafusion-tlp)
+
+- **2024-03-06** [Blog: Announcing Apache Arrow DataFusion Comet](https://datafusion.apache.org/blog/2024/03/06/comet-donation)
+
 - **2025-03-21** [Blog: Efficient Filter Pushdown in Parquet](https://datafusion.apache.org/blog/2025/03/21/parquet-pushdown/)
 
 - **2025-03-20** [Blog: Parquet Pruning in DataFusion: Read Only What Matters](https://datafusion.apache.org/blog/2025/03/20/parquet-pruning/)

docs/source/user-guide/sql/data_types.md

@@ -25,6 +25,11 @@ execution. The SQL types from
 are mapped to [Arrow data types](https://docs.rs/arrow/latest/arrow/datatypes/enum.DataType.html) according to the following table.
 This mapping occurs when defining the schema in a `CREATE EXTERNAL TABLE` command or when performing a SQL `CAST` operation.
 
+For background on extension types and custom metadata, see the
+[Implementing User Defined Types and Custom Metadata in DataFusion] blog.
+
+[implementing user defined types and custom metadata in datafusion]: https://datafusion.apache.org/blog/2025/09/21/custom-types-using-metadata
+
 You can see the corresponding Arrow type for any SQL expression using
 the `arrow_typeof` function. For example: