Introspection

These table functions inspect schemas, file lists and statistics. They read no dataset rows. Use them to explore an unfamiliar catalog before you write a query.

read_<format>_schema

read_parquet_schema(glob_paths)
read_geoparquet_schema(glob_paths)
read_csv_schema(glob_paths, delimiter, infer_records)
read_arrow_schema(glob_paths)
read_netcdf_schema(glob_paths)
read_hdf5_schema(glob_paths)
read_zarr_schema(glob_paths)
read_atlas_schema(glob_paths, dimensions)
read_tiff_schema(glob_paths)
read_bbf_schema(glob_paths)
read_delta_schema(location)
read_iceberg_schema(location)
read_odv_ascii_schema(glob_paths)

Every read_* reader has a _schema counterpart. It returns the Arrow schema of the files that reader would open, one row per column, without a scan of their data. The arguments match the reader it wraps.

The output is always the same three columns:

Column	Type	Description
column_name	TEXT	The column name
data_type	TEXT	The Arrow data type
nullable	BOOLEAN	Whether the column accepts nulls

-- Single path or glob
SELECT * FROM read_netcdf_schema('argo/**/*.nc');

SELECT * FROM read_parquet_schema('obs/*.parquet');

-- A list, to inspect the combined schema across several sources
SELECT * FROM read_parquet_schema(['obs/2023/*.parquet', 'obs/2024/*.parquet']);

-- Compose it like any other table
SELECT column_name FROM read_netcdf_schema('argo/**/*.nc')
WHERE data_type LIKE 'Timestamp%';

list_datasets

list_datasets()

Lists every file in the dataset storage root of Beacon. Returns one row for each file.

Column	Type	Description
file_name	TEXT	The path, relative to the storage root
file_format	TEXT	The format that Beacon detects

SELECT * FROM list_datasets()

-- Find all NetCDF files
SELECT file_name FROM list_datasets() WHERE file_format = 'nc'

view_dataset_statistics

view_dataset_statistics(path)

Returns the minimum and maximum of each column of one file. Beacon reads the statistics from the cache. If the cache holds nothing, Beacon computes them on demand.

Column	Type	Description
column_name	TEXT	The column name
data_type	TEXT	The data type of the column
min_value	TEXT	The minimum value. NULL if Beacon does not know it.
max_value	TEXT	The maximum value. NULL if Beacon does not know it.
is_exact	BOOLEAN	true if the statistics are exact

SELECT * FROM view_dataset_statistics('argo/2024/R6900001.nc')

view_external_table_statistics

view_external_table_statistics(table_name)

Returns the statistics of every file under an external table. Use it to see which files have cached statistics. It also gives their value ranges.

Column	Type	Description
path	TEXT	The file path
file_size	UINT64	The file size in bytes
cached	BOOLEAN	true if the cache holds statistics for this file
column_name	TEXT	The column name. NULL if the cache holds nothing.
data_type	TEXT	The data type of the column
min_value	TEXT	The minimum value
max_value	TEXT	The maximum value
is_exact	BOOLEAN	true if the statistics are exact

SELECT * FROM view_external_table_statistics('ocean_profiles')

-- Find files with no cached statistics
SELECT path FROM view_external_table_statistics('ocean_profiles')
WHERE cached = false

view_statistics_cache

view_statistics_cache()

Streams every entry of the global file statistics cache. Beacon checks each row against the object store. The is_valid flag shows two things: the file still exists, and its size matches.

Column	Type	Description
path	TEXT	The file path
file_size	UINT64	The file size in bytes
is_valid	BOOLEAN	true if the cache entry is still valid
column_name	TEXT	The column name
data_type	TEXT	The data type of the column
min_value	TEXT	The minimum value
max_value	TEXT	The maximum value
is_exact	BOOLEAN	true if the statistics are exact

SELECT * FROM view_statistics_cache()

-- Find stale cache entries
SELECT path FROM view_statistics_cache() WHERE is_valid = false