Overview of Data Unloading¶
Similar to data loading, Snowflake supports bulk export (i.e. unload) of data from a database table into flat, delimited text files.
In this Topic:
Data Unloading Process¶
As illustrated in the diagram above, the process for unloading data into files is the same as the loading process, except in reverse:
Use the COPY INTO location command to copy the data from the Snowflake database table into one or more files in a Snowflake or external staging location:
This step requires an active virtual warehouse. The warehouse provides the compute resources to write rows from the table.
Download the file from the location:
Data Unloading Using Queries¶
Snowflake supports specifying a SELECT statement instead of a table in the COPY INTO location command. The results of the query are written to one or more files as specified in the command and the file(s) are stored in the specified location (internal or external).
SELECT statements in COPY INTO location support the full syntax and semantics of Snowflake SQL queries, including JOIN clauses, which enables downloading data from multiple tables.
Data Unloading into Single or Multiple Files¶
The COPY INTO location command provides a copy option (SINGLE) for unloading data into a single file or multiple files. The default is SINGLE = FALSE (i.e. unload into multiple files).
Snowflake assigns each file a unique name. The location path specified for
the command can contain a filename prefix that is assigned to all the data files
generated. If a prefix is not specified, Snowflake prefixes the generated
Snowflake appends a suffix that ensures each file name is unique across
parallel execution threads; e.g.
When unloading data into multiple files, use the MAX_FILE_SIZE copy option to specify the maximum size of each file created.