Introduction to Snowflake's GENERATOR Function

The Snowflake GENERATOR function is a powerful tool for creating synthetic rows of data based on a specified number of rows, a specified generation period, or both. This system-defined table function enables users to generate virtual tables with a specified number of rows, which can be useful for queries that require a large amount of data.

Syntax and Usage Notes

The syntax for the GENERATOR function is as follows:

GENERATOR(ROWCOUNT => <count> [ , TIMELIMIT => <sec> ] )
GENERATOR( [ TIMELIMIT => <sec> ] )

The ROWCOUNT and TIMELIMIT parameters are non-negative integer constants. If only ROWCOUNT is specified, the resulting table will contain the specified number of rows. If only TIMELIMIT is specified, the query will run for the specified number of seconds, generating as many rows as possible within the time frame.

Key Points to Note

• If both ROWCOUNT and TIMELIMIT are specified, the function will generate rows until either the row count is reached or the time limit is exceeded.
• If ROWCOUNT or TIMELIMIT is null, it will be ignored.
• If both parameters are omitted, the GENERATOR function will return 0 rows.
• The content of the rows is determined by the functions in the projection clause, not by the GENERATOR function itself.

Examples of Using the GENERATOR Function

The following examples demonstrate how to use the GENERATOR function to generate synthetic rows of data.

Example 1: Generating 10 Rows

SELECT seq4(), uniform(1, 10, RANDOM(12)) 
FROM TABLE(GENERATOR(ROWCOUNT => 10)) v 
ORDER BY 1;

This query generates 10 rows with a sequence of 4-byte integers and a random value between 1 and 10.

Example 2: Generating Rows with a Constant Seed

SELECT seq4(), uniform(1, 10, 42) 
FROM TABLE(GENERATOR(ROWCOUNT => 10)) v 
ORDER BY 1;

This query generates 10 rows with a sequence of 4-byte integers and a constant value of 10.

Example 3: Omitting Both ROWCOUNT and TIMELIMIT

SELECT seq4(), uniform(1, 10, RANDOM(12)) 
FROM TABLE(GENERATOR()) v 
ORDER BY 1;

This query returns 0 rows because both ROWCOUNT and TIMELIMIT are omitted.

Example 4: Using the TIMELIMIT Parameter

SELECT COUNT(seq4()) 
FROM TABLE(GENERATOR(TIMELIMIT => 10)) v;

This query generates rows for 10 seconds and returns the count of rows generated.

Conclusion

The Snowflake GENERATOR function is a powerful tool for generating synthetic rows of data. By understanding the syntax and usage notes, users can leverage this function to create virtual tables with a specified number of rows, which can be useful for a variety of use cases. For more information on the GENERATOR function and other Snowflake features, visit the Snowflake documentation.

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• Snowflake Developer Center
• Snowflake Community Forum
• Snowflake Blog