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 three 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.

Directory Paths

The read_parquet function accepts a local directory path and recursively reads files with the .parquet extension, including files in subdirectories:

SELECT *
FROM read_parquet('dir');

This reads the same files as read_parquet('dir/**/*.parquet'). A trailing slash on the directory path is optional. In contrast, read_parquet('dir/*.parquet') reads only files directly inside dir.

Files with other extensions are ignored by directory discovery, even if they contain Parquet data. To read those files, supply their filenames explicitly. If the directory contains no matching files, the query raises an error.

Directory paths do not change how schemas are combined. When files have different columns, use union_by_name = true as described in combining schemas.

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.

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');

Handling Patterns That Match No Files

If a glob pattern does not match any files, the read functions raise an error:

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

IO Error:
No files found that match the pattern "test/*.parquet"

To handle this case gracefully, use the glob function to check whether any files match before reading. Unlike the read functions, glob returns an empty result instead of raising an error when nothing matches:

SELECT count(*) AS matches
FROM glob('test/*.parquet');

Your application can then skip the read when matches is 0.

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);

The filename argument also accepts a string (e.g., filename = 'input_file'). When provided, the string is used as the name of the added column. This is useful when the source data already contains a filename column and you want to avoid a name collision.

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('*');