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- COPY Statement 14539
- Examples Read a CSV file into the lineitem table, using auto-detected CSV options: COPY lineitem FROM 'lineitem.csv'; Read a CSV file into the lineitem table, using manually specified CSV options: COPY lineitem FROM 'lineitem.csv' (DELIMITE
...the same set of options as COPY ... FROM , however, in the case of COPY ... TO the options specify how the file should be written to disk. Any file created by COPY ... TO can be copied back into the database by using COPY ... FROM with a similar set of...alled specifying either a table name, or a query. When a table name is specified, the contents of the entire table will be written into the resulting file. When a query is specified, the query is executed and the result of the query is written to the re...atements in CTEs, see Data-Modifying CTEs . COPY ... TO can also be used as a CTE body. The CTE returns the number of rows written. COPY ... FROM cannot be used as a CTE body. WITH copied(rows_written) AS ( COPY lineitem TO 'lineitem.csv' (FORMAT CSV, H... - https://man.mtool.work/duckdb/2.0/sql/statements/copy.html
- Relational API 12596
- The Relational API builds a query one step at a time from Python. A relation, a DuckDBPyRelation , is a piece of SQL text: the methods of the Transformation and Functions sections return a new relation whose text extends the one they were c
...thousands in numbers; it must differ from decimal . * encoding : str, keyword-only, default: None Only UTF-8 is accepted, written 'utf-8' or 'utf8' ; any other encoding raises BinderException . * parallel : bool, keyword-only, default: None Whether to...or.LINE_FEED , duckdb.CSVLineTerminator.CARRIAGE_RETURN_LINE_FEED , '\\n' and '\\r\\n' , the last two being escape text as written in Python; a string that holds the newline character itself, such as '\n' , is refused. * columns : dict[str, str], keywor...to include in the GROUP BY ; cannot be combined with window_spec . * window_spec : str, default: '' Window specification, written as OVER (PARTITION BY ... ORDER BY ...) ; cannot be combined with groups . * projected_columns : str, default: '' Comma-se... - https://man.mtool.work/duckdb/2.0/clients/python/relational_api.html
- Partitioned Writes 10538
- Examples Write a table to a Hive partitioned dataset of Parquet files: COPY orders TO 'orders' (FORMAT parquet, PARTITION_BY (year, month)); Write a table to a Hive partitioned dataset of CSV files, allowing overwrites: COPY orders TO 'orde
...E_EXTENSION 'csv.gz'); Partitioned Writes When the PARTITION_BY clause is specified for the COPY statement , the files are written in a Hive partitioned folder hierarchy. The target is the name of the root directory (in the example above: orders ). The...files are written in-order in the file hierarchy. Currently, one file is written per thread to each directory. orders ├── year=2021 │ ├── mo...tion Paths New As of DuckDB 2.0, the PARTITION_PATH option gives full control over the subdirectory that each partition is written to, replacing the default col=value Hive layout. By default, the PARTITION_BY clause writes each partition to a col=value... - https://man.mtool.work/duckdb/2.0/data/partitioning/partitioned_writes.html
- SAMPLE Clause 10538
- The SAMPLE clause allows you to run the query on a sample from the base table. This can significantly speed up processing of queries, at the expense of accuracy in the result. Samples can also be used to quickly see a snapshot of the data w
...ght after anything in the FROM clause" describes the logical point at which sampling takes effect, not where the clause is written. Syntactically, the USING SAMPLE clause appears at the end of the SELECT statement body: after the WHERE , GROUP BY , HAVI...NG , and QUALIFY clauses, and before ORDER BY and LIMIT . So it is written after grouping and filtering, but it is applied to the result of the FROM clause before those operations run. To sample an...individual table expression rather than the result of the entire FROM clause, use the TABLESAMPLE clause, which is written directly after the table expression it applies to. See Table Samples .... - https://man.mtool.work/duckdb/2.0/sql/query_syntax/sample.html
- Writing Tests 8972
- Development and Testing It is crucial that any new features that get added have correct tests that not only test the “happy path”, but also test edge cases and incorrect usage of the feature. In this section, we describe how DuckDB tests ar
...l discuss in Catch Tests . However, in most cases you should write your tests in plain SQL. Frameworks SQL tests should be written using the sqllogictest framework . C++ tests can be written using the Catch framework . Client Connector Tests DuckDB also...has tests for various client connectors. These are generally written in the relevant client language, and can be found in tools/*/tests . They also double as documentation of what should be d... - https://man.mtool.work/duckdb/2.0/dev/sqllogictest/writing_tests.html
- Samples 8334
- Samples are used to randomly select a subset of a dataset. Examples Select a sample of exactly 5 rows from tbl using reservoir sampling: SELECT * FROM tbl USING SAMPLE 5; Select a sample of approximately 10% of the table using system sampli
...NG SAMPLE clauses use the same internal syntax (sample size, method, and optional seed), but they differ in where they are written and what they sample. The TABLESAMPLE clause is written directly after a table expression, following its alias if one is p...resent, and samples only that table. The USING SAMPLE clause is written at the end of the SELECT statement body and samples the result of the entire FROM clause, after all joins have been resolv... - https://man.mtool.work/duckdb/2.0/sql/samples.html
- Metrics 8074
- DuckDB provides a set of metrics that can be used to monitor the performance and health of the database. Metrics are named ⟨group⟩.⟨metric⟩ , e.g., query.total_time or operator.timing . The set of collected metrics is controlled with the tr
...emory_allocated uint64 bytes The total memory allocated by the buffer manager io Metrics Metrics on the data read from and written to storage. Name Type Unit Description io.total_bytes_read uint64 bytes The total amount of bytes read from storage io.tot...al_bytes_written uint64 bytes The total amount of bytes written to storage storage Metrics Metrics on storage operations, such as attaching... - https://man.mtool.work/duckdb/2.0/dev/metrics.html
- Storage Versions and Format 7813
- Compatibility Backward Compatibility Backward compatibility refers to the ability of a newer DuckDB version to read storage files created by an older DuckDB version. Version 0.10 is the first release of DuckDB that supports backward compati
...les around and guarantees that you will be able to read the files without having to worry about which version the file was written with or having to convert files between versions. Forward Compatibility Forward compatibility refers to the ability of an...ersion setting specifies the minimum DuckDB version that should be able to read the database file. When database files are written with this option, the resulting files cannot be opened by older DuckDB released versions than the specified version. They...rsion , e.g., v1.5.0 . Error Message When Opening an Incompatible Database File When opening a database file that has been written by a different DuckDB version from the one you are using, the following error message may occur: Error: unable to open dat... - https://man.mtool.work/duckdb/2.0/internals/storage.html
- Community Extensions 7682
- Community-contributed extensions can be installed from the Community Extensions repository since summer 2024 . Please visit the “Community Extensions” section of the documentation for more details. Warning Community extensions are contribut
...ed by third parties. They are not written, audited, or maintained by DuckLabs, and they run with the same privileges as DuckDB itself. Signing proves only that an e... - https://man.mtool.work/duckdb/2.0/extensions/community_extensions.html
- Write User Defined Functions 7552
- Overview The JDBC driver can register user-defined functions (UDFs) written in Java, including scalar functions and table functions. This page covers building and registering both, from the simple functional-interface overloads to the vecto
...eeds per-thread state; the default returns null . apply writes rows into the output vectors and returns the number of rows written, with access to the bind, global-init, and local-init data. The engine calls it repeatedly until it returns 0 . import jav...bal init data, and the local init data. Call the function from SQL: FROM java_table_basic(42, param1 = 'foobar'); Rows are written through a DuckDBDataChunkWriter , the write-side counterpart to the DuckDBDataChunkReader used for reading results. Each o... - https://man.mtool.work/duckdb/2.0/clients/java/functions.html
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