--- title: "Csv@2" description: "Csv@2 — CSV files loaded into an in-memory DuckDB database, full SQL, no driver needed" url: "https://docs.justcat.it/reference/data-sources/providers/csv-2/" --- # Csv@2 ## Connects to CSV files. CAT loads each file into a table of an in-memory DuckDB database — once for each executing thread (by default once only) — and the queries run against those tables. The data is removed from memory after all tests are evaluated. ## Example **Properties** Name : FinancialData Provider : Csv@2 Technology : Csv Connection string : DataToTest\Invoices.csv **YAML** ```yaml Data sources: - Name: FinancialData Provider: Csv@2 Technology: Csv Connection string: DataToTest\Invoices.csv ``` Each file becomes a table named `"".""` — here `"FinancialData"."Invoices"`. ## Connection string A path, or a list of paths, to CSV files — any of: * an absolute path to a CSV file; * a relative path to a CSV file — resolved against the directory of the `.cat.yaml` project file; * an absolute or relative path with the wildcard `*` — allowed only in the file name, no recursion into subdirectories; * several of the above, separated by commas. **Properties** Name : My CSV data Provider : Csv@2 Technology : Csv Connection string : ``` DataToTest\*.csv, D:\Export\Financial\Invoices-2024.csv ``` **YAML** ```yaml Data sources: - Name: My CSV data Provider: Csv@2 Technology: Csv Connection string: > DataToTest\*.csv, D:\Export\Financial\Invoices-2024.csv ``` Every file that matches is loaded into a separate table; the files are **not** combined into one. If `DataToTest` holds `Summary-2023.csv` and `Summary-2024.csv`, a query can combine them itself: ```sql SELECT * FROM "My CSV data"."Summary-2023" UNION ALL SELECT * FROM "My CSV data"."Summary-2024" ``` ## Settings | Setting | Default | Meaning | |---|---|---| | `Settings` | `auto_detect = true` | Options for DuckDB's CSV reader, written as one comma-separated list — delimiter, header row, compression, quoting, types … Every option of DuckDB `read_csv` is accepted; CAT hands the string over as it is. | **Properties** Name : FinancialData Provider : Csv@2 Technology : Csv Connection string : DataToTest\Invoices.csv Settings : delim = '|', header = true, compression = 'gzip' **YAML** ```yaml Data sources: - Name: FinancialData Provider: Csv@2 Technology: Csv Connection string: DataToTest\Invoices.csv Settings: delim = '|', header = true, compression = 'gzip' ``` ## Query One SQL statement in DuckDB's dialect against the loaded tables — table names are `"".""`, quoted when they contain spaces or a hyphen. Because the data sits in a database, the whole language is available: joins, grouping, CTEs, window functions, functions for dates, strings and numbers. What that looks like in practice — `SELECT`, joins and set operations, expressions, functions — is in [Query CSV and Excel data with DuckDB SQL](https://docs.justcat.it/how-to-guides/data-platforms/query-csv-and-excel-with-duckdb-sql/ "Query CSV and Excel data with DuckDB SQL"); the full reference is the DuckDB SQL documentation. ## Prerequisites DuckDB ships with CAT; Windows and Linux alike. Two things must be in place on the machine: ### Microsoft Visual C++ Redistributable (Windows) A very common prerequisite used by much other software, so it is probably already installed. To verify or install it, go to Latest Microsoft Visual C++ Redistributable Version and download and install the "X64" version: ![Microsoft Visual C++ Redistributable web download link](visual-cpp-redistributable.png) If the installer shows a dialog with "Repair", "Uninstall" and "Close" buttons, just close it — the prerequisite is already there. Otherwise install it (next, next, next…). ### Internet connection DuckDB loads its extensions from http://extensions.duckdb.org. The URL has to be reachable — connect to the Internet and white-list it if needed. If you need to test CSV data offline, file a request using the "Get Help" button on the right of this site. ## Limitations * `Csv@2` cannot serve lists of test or data source definitions; `Csv@1` can. * Needs access to `extensions.duckdb.org` at start — see Prerequisites. ## Serving test and data source definitions `Csv@2` cannot serve lists of definitions; use [Csv@1](https://docs.justcat.it/reference/data-sources/providers/csv-1/ "Csv@1") for that. ## Related * [Technologies](https://docs.justcat.it/reference/data-sources/technologies/ "Technologies") — CSV file and the provider behind it. * [Csv@1](https://docs.justcat.it/reference/data-sources/providers/csv-1/ "Csv@1") — the simple CSV reader that also serves definition lists. * [Excel@2](https://docs.justcat.it/reference/data-sources/providers/excel-2/ "Excel@2") — the same DuckDB engine over workbooks. * [Query CSV and Excel data with DuckDB SQL](https://docs.justcat.it/how-to-guides/data-platforms/query-csv-and-excel-with-duckdb-sql/ "Query CSV and Excel data with DuckDB SQL") — the SQL you can write against the loaded tables, by example.