Table Functions

To register a table function, call one of the RegisterTableFunction overloads specifying the function name, input parameter type(s), callback for returning result set and a callback function that maps an item from the result map.

connection.RegisterTableFunction<string, int>("github_search", (parameters) =>
{
    var term = parameters[0].GetValue<string>();
    var stars = parameters[1].GetValue<int>();

    var client = new GitHubClient(new ProductHeaderValue("DuckDB-Table-Valued-Function"));

    var request = new SearchRepositoriesRequest(term)
    {
        Stars = new Octokit.Range(stars, SearchQualifierOperator.GreaterThan)
    };

    var result = client.Search.SearchRepo(request).ConfigureAwait(false).GetAwaiter().GetResult();

    return new TableFunction(new List<ColumnInfo>()
    {
        new ColumnInfo("name", typeof(string)),
        new ColumnInfo("description", typeof(string)),
        new ColumnInfo("stargazers", typeof(int)),
        new ColumnInfo("url", typeof(string)),
        new ColumnInfo("owner", typeof(string)),
    }, result.Items);
}, (item, writers, rowIndex) =>
{
    var repo = (Repository)item;
    writers[0].WriteValue(repo.Name, rowIndex);
    writers[1].WriteValue(repo.Description, rowIndex);
    writers[2].WriteValue(repo.StargazersCount, rowIndex);
    writers[3].WriteValue(repo.Url, rowIndex);
    writers[4].WriteValue(repo.Owner.Login, rowIndex);
});

In the example above we define a table function, github_search that takes two parameters: a string parameter that is used as a search term and an int that filters results by stargazers. The first callback, resultCallback, provides access to the parameters that the functions was invoked with and returns a TableFunction instance that describes the columns that our table function has and an IEnumerable<> that serves as a result set of the invocation. The second callback, mapperCallback will be invoked by DuckDB.NET for every item in the result that. In this callback you should use the provided IDuckDBDataWriter array to write the item back to DuckDB.

After registering the table function you can use just like any other table. For example, you can search for all DuckDB repositories with 400 stars or more with the following query:

var data = connection.Query<(string, string, int, string, string)>("SELECT * FROM github_search('duckdb', 400);");

Executing the above query produces the following result:

name description stargazers url owner
duckdb DuckDB is an analytical in-process SQL database management system 24115 https://api.github.com/repos/duckdb/duckdb duckdb
duckdb-wasm WebAssembly version of DuckDB 1272 https://api.github.com/repos/duckdb/duckdb-wasm duckdb
dbt-duckdb dbt (http://getdbt.com) adapter for DuckDB (http://duckdb.org) 916 https://api.github.com/repos/duckdb/dbt-duckdb duckdb
awesome-duckdb 🦆 A curated list of awesome DuckDB resources 1358 https://api.github.com/repos/davidgasquez/awesome-duckdb davidgasquez
go-duckdb go-duckdb provides a database/sql driver for the DuckDB database engine. 716 https://api.github.com/repos/marcboeker/go-duckdb marcboeker
duckdb-rs Ergonomic bindings to duckdb for Rust 501 https://api.github.com/repos/duckdb/duckdb-rs duckdb
pg_duckdb DuckDB-powered Postgres for high performance apps & analytics. 1575 https://api.github.com/repos/duckdb/pg_duckdb duckdb
DuckDB.NET Bindings and ADO.NET Provider for DuckDB 430 https://api.github.com/repos/Giorgi/DuckDB.NET Giorgi
duckdb_spatial 483 https://api.github.com/repos/duckdb/duckdb_spatial duckdb
sql-studio SQL Database Explorer [SQLite, libSQL, PostgreSQL, MySQL/MariaDB, DuckDB, ClickHouse] 2330 https://api.github.com/repos/frectonz/sql-studio frectonz
nba-monte-carlo Monte Carlo simulation of the NBA season, leveraging dbt, duckdb and evidence.dev 446 https://api.github.com/repos/matsonj/nba-monte-carlo matsonj
logica Logica is a logic programming language that compiles to SQL. It runs on DuckDB, Google BigQuery, PostgreSQL and SQLite. 1767 https://api.github.com/repos/EvgSkv/logica EvgSkv
WhatTheDuck WhatTheDuck is an open-source web application built on DuckDB. It allows users to upload CSV files, store them in tables, and perform SQL queries on the data. 515 https://api.github.com/repos/incentius-foss/WhatTheDuck incentius-foss
mosaic An extensible framework for linking databases and interactive views. 834 https://api.github.com/repos/uwdata/mosaic uwdata
lance Modern columnar data format for ML and LLMs implemented in Rust. Convert from parquet in 2 lines of code for 100x faster random access, vector index, and data versioning. Compatible with Pandas, DuckDB, Polars, Pyarrow, and PyTorch with more integrations coming.. 3932 https://api.github.com/repos/lancedb/lance lancedb
tad A desktop application for viewing and analyzing tabular data 3174 https://api.github.com/repos/antonycourtney/tad antonycourtney
narwhals Lightweight and extensible compatibility layer between dataframe libraries! 557 https://api.github.com/repos/narwhals-dev/narwhals narwhals-dev
scratchdata Scratch is a swiss army knife for big data. 1098 https://api.github.com/repos/scratchdata/scratchdata scratchdata
ingestr ingestr is a CLI tool to copy data between any databases with a single command seamlessly. 2547 https://api.github.com/repos/bruin-data/ingestr bruin-data
splink Fast, accurate and scalable probabilistic data linkage with support for multiple SQL backends 1359 https://api.github.com/repos/moj-analytical-services/splink moj-analytical-services
FreeSql 🦄 .NET aot orm, C# orm, VB.NET orm, Mysql orm, Postgresql orm, SqlServer orm, Oracle orm, Sqlite orm, Firebird orm, 达梦 orm, 人大金仓 orm, 神通 orm, 翰高 orm, 南大通用 orm, 虚谷 orm, 国产 orm, Clickhouse orm, DuckDB orm, TDengine orm, QuestDB orm, MsAccess orm. 4113 https://api.github.com/repos/dotnetcore/FreeSql dotnetcore
inline-sql 🪄 Inline SQL in any Python program 418 https://api.github.com/repos/ekzhang/inline-sql ekzhang
ibis the portable Python dataframe library 5282 https://api.github.com/repos/ibis-project/ibis ibis-project
sqlglot Python SQL Parser and Transpiler 6701 https://api.github.com/repos/tobymao/sqlglot tobymao
evidence Business intelligence as code: build fast, interactive data visualizations in pure SQL and markdown 4392 https://api.github.com/repos/evidence-dev/evidence evidence-dev
qstudio qStudio - Free SQL Analysis Tool 568 https://api.github.com/repos/timeseries/qstudio timeseries
WrenAI 🚀 An open-source SQL AI (Text-to-SQL) Agent that empowers data, product teams to chat with their data, and directly connect with Excel and Google Sheets.🤘 2016 https://api.github.com/repos/Canner/WrenAI Canner
BemiDB Postgres read replica optimized for analytics 747 https://api.github.com/repos/BemiHQ/BemiDB BemiHQ
pretzelai The modern replacement for Jupyter Notebooks 2005 https://api.github.com/repos/pretzelai/pretzelai pretzelai
rill Rill is a tool for effortlessly transforming data sets into powerful, opinionated dashboards using SQL. BI-as-code. 1714 https://api.github.com/repos/rilldata/rill rilldata
latitude Developer-first embedded analytics 877 https://api.github.com/repos/latitude-dev/latitude latitude-dev
vulcan-sql Data API Framework for AI Agents and Data Apps 641 https://api.github.com/repos/Canner/vulcan-sql Canner
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