Search Shortcut cmd + k | ctrl + k
Search cmd+k ctrl+k
1.0 (stable)
Reading Multiple Files

DuckDB can read multiple files of different types (CSV, Parquet, JSON files) at the same time using either the glob syntax, or by providing a list of files to read. See the combining schemas page for tips on reading files with different schemas.

CSV

Read all files with a name ending in .csv in the folder dir.

SELECT * FROM 'dir/*.csv';

Read all files with a name ending in .csv, two directories deep.

SELECT * FROM '*/*/*.csv';

Read all files with a name ending in .csv, at any depth in the folder dir.

SELECT * FROM 'dir/**/*.csv';

Read the CSV files flights1.csv and flights2.csv.

SELECT * FROM read_csv(['flights1.csv', 'flights2.csv']);

Read the CSV files flights1.csv and flights2.csv, unifying schemas by name and outputting a filename column.

SELECT * FROM read_csv(['flights1.csv', 'flights2.csv'], union_by_name = true, filename = true);

Parquet

Read all files that match the glob pattern.

SELECT * FROM 'test/*.parquet';

Read 3 Parquet files and treat them as a single table.

SELECT * FROM read_parquet(['file1.parquet', 'file2.parquet', 'file3.parquet']);

Read all Parquet files from two specific folders.

SELECT * FROM read_parquet(['folder1/*.parquet', 'folder2/*.parquet']);

Read all Parquet files that match the glob pattern at any depth.

SELECT * FROM read_parquet('dir/**/*.parquet');

Multi-File Reads and Globs

DuckDB can also read a series of Parquet files and treat them as if they were a single table. Note that this only works if the Parquet files have the same schema. You can specify which Parquet files you want to read using a list parameter, glob pattern matching syntax, or a combination of both.

List Parameter

The read_parquet function can accept a list of filenames as the input parameter.

Read three Parquet files and treat them as a single table.

SELECT * FROM read_parquet(['file1.parquet', 'file2.parquet', 'file3.parquet']);

Glob Syntax

Any file name input to the read_parquet function can either be an exact filename, or use a glob syntax to read multiple files that match a pattern.

Wildcard Description
* matches any number of any characters (including none)
** matches any number of subdirectories (including none)
? matches any single character
[abc] matches one character given in the bracket
[a-z] matches one character from the range given in the bracket

Note that the ? wildcard in globs is not supported for reads over S3 due to HTTP encoding issues.

Here is an example that reads all the files that end with .parquet located in the test folder:

Read all files that match the glob pattern.

SELECT * FROM read_parquet('test/*.parquet');

List of Globs

The glob syntax and the list input parameter can be combined to scan files that meet one of multiple patterns.

Read all Parquet files from 2 specific folders.

SELECT * FROM read_parquet(['folder1/*.parquet', 'folder2/*.parquet']);

DuckDB can read multiple CSV files at the same time using either the glob syntax, or by providing a list of files to read.

Filename

The filename argument can be used to add an extra filename column to the result that indicates which row came from which file. For example:

SELECT * FROM read_csv(['flights1.csv', 'flights2.csv'], union_by_name = true, filename = true);
FlightDate OriginCityName DestCityName UniqueCarrier filename
1988-01-01 New York, NY Los Angeles, CA NULL flights1.csv
1988-01-02 New York, NY Los Angeles, CA NULL flights1.csv
1988-01-03 New York, NY Los Angeles, CA AA flights2.csv

Since v0.10.2, it is possible to specify the name of the filename column using the filename argument:

SELECT * FROM read_csv(['flights1.csv', 'flights2.csv'], union_by_name = true, filename = "my_filename_column");
FlightDate UniqueCarrier OriginCityName DestCityName my_filename_column
1988-01-01 AA New York, NY Los Angeles, CA flights1.csv
1988-01-02 AA New York, NY Los Angeles, CA flights1.csv
1988-01-03 AA New York, NY Los Angeles, CA flights2.csv

Glob Function to Find Filenames

The glob pattern matching syntax can also be used to search for filenames using the glob table function. It accepts one parameter: the path to search (which may include glob patterns).

Search the current directory for all files.

SELECT * FROM glob('*');
file
duckdb.exe
test.csv
test.json
test.parquet
test2.csv
test2.parquet
todos.json

Pages in This Section

About this page

Last modified: 2024-06-12