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- Samples 13700
- 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 sampling
...in the sample with that probability. If your table contains fewer than ~10k rows, it makes sense to specify the bernoulli sampling option instead, which applies the probability to each row independently. Even then, you'll sometimes get more and sometime...t 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 table using bernoulli sampling: SELECT * FROM tbl USING SAMPLE 10 PERC...ENT (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 sa... - https://man.mtool.work/duckdb/2.0/sql/samples.html
- SAMPLE Clause 9272
- 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
...s). See the SAMPLE page for more information. Examples Select a sample of 1% of the addresses table using default (system) sampling: SELECT * FROM addresses USING SAMPLE 1%; Select a sample of 1% of the addresses table using bernoulli sampling: SELECT *...ent above that the sample clause is "applied right 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 sta... - https://man.mtool.work/duckdb/2.0/sql/query_syntax/sample.html
- Profile and Monitor 8422
- Overview The JDBC driver exposes several ways to observe a running or completed query: cancelling and timing out queries, polling query progress, retrieving profiling output, and emitting memory-usage events through Java Flight Recorder . T
...the given value. The JDBC property is only an enable and label switch. It does not control whether JFR is recording or the sampling period; those are governed by the JFR recording settings. Controlling the Period and Enabled State The sampling rate and e... - https://man.mtool.work/duckdb/2.0/clients/java/profiling.html
- CSV Auto Detection 8350
- When using read_csv , the system tries to automatically infer how to read the CSV file using the CSV sniffer . This step is necessary because CSV files are not self-describing and come in many different dialects. The auto-detection works ro
...rameter. The default sample size is 20,480 rows. Setting the sample_size parameter to -1 means the entire file is read for sampling: SELECT * FROM read_csv('my_csv_file.csv', sample_size = -1); The way sampling is performed depends on the type of file. I... - https://man.mtool.work/duckdb/2.0/data/csv/auto_detection.html
- Data Ingestion 8169
- This page contains examples for data ingestion to Python using DuckDB. First, import the DuckDB package: import duckdb Then, proceed with any of the following sections. CSV Files CSV files can be read using the read_csv function, called eit
...m within Python or directly from within SQL. By default, the read_csv function attempts to auto-detect the CSV settings by sampling from the provided file. Read from a file using fully auto-detected settings: duckdb.read_csv("example.csv") Read multiple... - https://man.mtool.work/duckdb/2.0/clients/python/data_ingestion.html
- Metrics 8169
- 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
...optimizer.top_n , optimizer.compressed_materialization , optimizer.duplicate_groups , optimizer.reorder_filter , optimizer.sampling_pushdown , optimizer.join_filter_pushdown , optimizer.extension , optimizer.materialized_cte , optimizer.aggregate_functio... - https://man.mtool.work/duckdb/2.0/dev/metrics.html
- Aggregate Functions 8079
- Examples Produce a single row containing the sum of the amount column: SELECT sum(amount) FROM sales; Produce one row per unique region, containing the sum of amount for each group: SELECT region, sum(amount) FROM sales GROUP BY region; Ret
...ered Space-Saving. reservoir_quantile(x, quantile, sample_size = 8192) Calculates the approximate quantile using reservoir sampling, the sample size is optional and uses 8192 as a default size. reservoir_quantile(A, 0.5, 1024) Statistical Aggregates The... - https://man.mtool.work/duckdb/2.0/sql/functions/aggregates.html
- Relational API 8043
- 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
...e = None) -> DuckDBPyRelation A random subset: n rows, or percent of them, with seed repeating a draw. See Samples for the sampling methods. A fixed seed gives the same sample on every run only when DuckDB runs on one thread. Parameters n : int, default:... - https://man.mtool.work/duckdb/2.0/clients/python/relational_api.html
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