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DuckDB allows directly reading files via the read_text
and read_blob
functions.
These functions accept a filename, a list of filenames or a glob pattern, and output the content of each file as a VARCHAR
or BLOB
, respectively, as well as additional metadata such as the file size and last modified time.
read_text
The read_text
table function reads from the selected source(s) to a VARCHAR
. Each file results in a single row with the content
field holding the entire content of the respective file.
SELECT size, parse_path(filename), content
FROM read_text('test/sql/table_function/files/*.txt');
size | parse_path(filename) | content |
---|---|---|
12 | [test, sql, table_function, files, one.txt] | Hello World! |
2 | [test, sql, table_function, files, three.txt] | 42 |
10 | [test, sql, table_function, files, two.txt] | Foo Bar\nFöö Bär |
The file content is first validated to be valid UTF-8. If read_text
attempts to read a file with invalid UTF-8, an error is thrown suggesting to use read_blob
instead.
read_blob
The read_blob
table function reads from the selected source(s) to a BLOB
:
SELECT size, content, filename
FROM read_blob('test/sql/table_function/files/*');
size | content | filename |
---|---|---|
178 | PK\x03\x04\x0A\x00\x00\x00\x00\x00\xACi=X\x14t\xCE\xC7\x0A… | test/sql/table_function/files/four.blob |
12 | Hello World! | test/sql/table_function/files/one.txt |
2 | 42 | test/sql/table_function/files/three.txt |
10 | F\xC3\xB6\xC3\xB6 B\xC3\xA4r | test/sql/table_function/files/two.txt |
Schema
The schemas of the tables returned by read_text
and read_blob
are identical:
DESCRIBE FROM read_text('README.md');
column_name | column_type | null | key | default | extra |
---|---|---|---|---|---|
filename | VARCHAR | YES | NULL | NULL | NULL |
content | VARCHAR | YES | NULL | NULL | NULL |
size | BIGINT | YES | NULL | NULL | NULL |
last_modified | TIMESTAMP | YES | NULL | NULL | NULL |
Handling Missing Metadata
In cases where the underlying filesystem is unable to provide some of this data due (e.g., because HTTPFS can't always return a valid timestamp), the cell is set to NULL
instead.
Support for Projection Pushdown
The table functions also utilize projection pushdown to avoid computing properties unnecessarily. So you could e.g., use this to glob a directory full of huge files to get the file size in the size column, as long as you omit the content column the data won't be read into DuckDB.