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- Samples 14512
- 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
...s less than the specified percentage of the number of rows, but it is much less likely that you get no rows at all. To get exactly 10% of rows (up to rounding), you must use the reservoir sampling option. Select a sample of approximately 10% of the tabl...e using bernoulli sampling: SELECT * FROM tbl USING SAMPLE 10 PERCENT (bernoulli); Select a sample of exactly 10% (up to rounding) of the table using reservoir sampling: SELECT * FROM tbl USING SAMPLE 10 PERCENT (reservoir); Select...a sample of exactly 50 rows of the table using reservoir sampling with a fixed seed (100): SELECT * FROM tbl USING SAMPLE reservoir(50 ROWS) R... - https://man.mtool.work/duckdb/2.0/sql/samples.html
- Join Operations 11776
- How to Force a Join Order DuckDB has a cost-based query optimizer, which uses statistics in the base tables (stored in a DuckDB database or Parquet files) to estimate the cardinality of operations. Turn off the Join Order Optimizer To turn
...ROP TABLE IF EXISTS t2; Configuring the Join Order Optimizer DuckDB's join order optimizer computes the optimal join order exactly using a dynamic programming algorithm. As the number of tables in a join grows, exact enumeration becomes expensive, so fo...en this happens: joins with at least this many tables are ordered approximately, while joins with fewer tables are ordered exactly. The default value is 12. For example, to use the exact algorithm for joins of up to 15 tables, run: SET approximate_join_... - https://man.mtool.work/duckdb/2.0/guides/performance/join_operations.html
- Appender 9550
- Use an appender to insert rows that your Python code produces. It collects rows and writes them together in one SQL statement; this is called flushing. The with block below flushes on successful exit: import duckdb con = duckdb.connect() co
...generated columns. append_row takes one value per column, and append_rows takes any iterable of rows. Values are converted exactly as executemany parameters are. To append to some of the columns, list them in columns . The other columns take their defau...ROM stock ORDER BY sku").fetchall()) [('gadget', 0), ('widget', 10)] upsert runs an INSERT OR REPLACE , so the table needs exactly one primary key or unique constraint. It takes columns like an insert; on a conflict, only the listed columns change. upda... - https://man.mtool.work/duckdb/2.0/clients/python/appender.html
- Troubleshoot 8547
- Overview This page collects common issues encountered when using DuckDB-Wasm, together with their workarounds. If you run into a problem that is not covered here, search the duckdb-wasm issue tracker on GitHub. Network Error When Querying R
...://some.url.com⟩' , the GET requests for the extension files must be CORS enabled for the browser to allow the connection, exactly as for remote data files above. Extensions remain signed regardless of where they are served, so copying an extension to a... - https://man.mtool.work/duckdb/2.0/clients/wasm/troubleshoot.html
- Delta Extension 8547
- The delta extension adds support for the Delta Lake open-source storage format . It is built using the Delta Kernel . The extension reads Delta tables, local and remote, and writes them: it can create tables and append to them. For implemen
...* FROM delta_scan('file:///⟨path⟩'); Attaching Tables A Delta table can also be attached as a database. The database holds exactly one table, with the same name as the database, so my_table and my_table.my_table refer to the same table: ATTACH 'file:///...ailable, e.g., a service principal in the environment and the Azure CLI, credential loading may be inconsistent. Configure exactly one credential type in the chain of your secret. Since v1.5.6, the delta extension supports Azure workload identity (for e... - https://man.mtool.work/duckdb/2.0/core_extensions/delta.html
- sqllogictest Introduction 8309
- For testing plain SQL, we use an extended version of the SQL logic test suite, adopted from SQLite . Every test is a single self-contained file located in the test/sql directory. To run tests located outside of the default test directory, s
..., except those involving larger datasets (more than ~10-100 rows). Editors & Syntax Highlighting The sqllogictests are not exactly an industry standard, but several other systems have adopted them as well. Parsing sqllogictests is intentionally simple.... - https://man.mtool.work/duckdb/2.0/dev/sqllogictest/intro.html
- Vectors 8055
- Vectors represent a horizontal slice of a column. They hold a number of values of a specific type, similar to an array. Vectors are the core data representation used in DuckDB. Vectors are typically stored within data chunks . The vector an
...s must be checked using the validity mask again. Arrays Arrays are nested types that contain a single child type, repeated exactly array_size times per row. Think of them like a fixed-size array in C. Arrays work exactly the same as lists, except the le... - https://man.mtool.work/duckdb/2.0/clients/c/vector.html
- Go Client 8055
- The latest stable release of the DuckDB Go client bundles DuckDB 2.0.0. Its own version tag encodes that DuckDB version; see Versioning below. The DuckDB Go client, duckdb-go , is a SQL driver that conforms to Go's built-in database/sql int
...database, and a file path opens (or creates) a persistent database. From there, Exec , Query , and QueryRow run statements exactly as they do for any database/sql driver: package main import ( "database/sql" "errors" "fmt" "log" _ "github.com/duckdb/duc... - https://man.mtool.work/duckdb/2.0/clients/go/overview.html
- Run Queries 8055
- Overview A Connection runs SQL through two families of methods: The execute_* methods ( execute() and execute_batch() ) send statements that do not return rows, such as INSERT or DDL, and report the number of affected rows. The query_* meth
...by name with row.get("name") . This example follows the crate's basic example . Reading a Single Row When a query returns exactly one row, Connection::query_row() runs it and applies a closure to that row in one call, without preparing a statement by h... - https://man.mtool.work/duckdb/2.0/clients/rust/querying.html
- Configuration 8055
- DuckDB has a number of configuration options that can be used to change the behavior of the system. The configuration options can be set using either the SET statement or the PRAGMA statement . They can be reset to their original values usi
...e_join_order_threshold The minimum number of tables in a join to determine the optimal join order approximately instead of exactly. UBIGINT 12 arrow_large_buffer_size Whether Arrow buffers for strings, blobs, UUIDs and bits should be exported using larg...e sized: AUTO lets each reader choose, GRID reads the aligned blocks of the cache block size around each read, EXACT reads exactly the requested bytes. Reads of files that are not cached are always exact. VARCHAR AUTO external_file_cache_spill Whether e... - https://man.mtool.work/duckdb/2.0/configuration/overview.html
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