How to capture Python stored procedure return value in Snowflake variable

[Zack_88Surf]

I’m trying to store the return value from a Python stored procedure into a SQL variable in Snowflake, but I keep getting syntax errors. Here’s what I’m working with:

CREATE OR REPLACE TEMPORARY PROCEDURE process_data()
RETURNS STRING
LANGUAGE PYTHON
RUNTIME_VERSION = 3.11
HANDLER = 'execute_task'
AS
$$
def execute_task():
    return "Task completed successfully"
$$
;

DECLARE result_var STRING;

BEGIN
  EXECUTE IMMEDIATE 'CALL process_data()' INTO :result_var;
  RETURN result_var;
END;

Show VARIABLES;

The error messages I’m getting are about unexpected ‘INTO’ and ‘RETURN’ syntax. I want the result_var variable to contain the string "Task completed successfully" that gets returned from my Python function. What’s the correct way to capture a Python procedure’s return value in a Snowflake SQL variable?

[Alex_Dynamo]

The Problem:

You’re attempting to store the return value of a Python stored procedure in a Snowflake SQL variable using EXECUTE IMMEDIATE and INTO, resulting in syntax errors. Your goal is to capture the string "Task completed successfully" returned by the Python function into the result_var variable.

Understanding the “Why” (The Root Cause):

Snowflake’s EXECUTE IMMEDIATE statement doesn’t work with INTO in the same way as some other database systems. EXECUTE IMMEDIATE is primarily designed for executing dynamic SQL statements, not for directly capturing the return value of a stored procedure. The INTO clause is used for assigning the results of a SELECT statement to variables, not the output of a stored procedure call. Python stored procedures in Snowflake return values through their return statements within the Python handler, which needs to be handled differently. Directly attempting to use EXECUTE IMMEDIATE and INTO causes the unexpected syntax errors.

Step-by-Step Guide:

Step 1: Use SET for Direct Assignment. The simplest and most efficient method is to use the SET command to directly assign the return value of your procedure to the SQL variable. Avoid EXECUTE IMMEDIATE entirely in this scenario.

CREATE OR REPLACE TEMPORARY PROCEDURE process_data()
RETURNS STRING
LANGUAGE PYTHON
RUNTIME_VERSION = 3.11
HANDLER = 'execute_task'
AS
$$
def execute_task():
    return "Task completed successfully"
$$
;

DECLARE result_var STRING;

SET result_var = process_data();

SELECT $result_var; -- Access and display the value of the variable

Step 2: Understand Variable Access. Note the use of $result_var to access the value stored in the variable after it’s been set. The dollar sign ($) prefix is crucial for referencing variables within Snowflake SQL statements.

Step 3 (Optional): Using a SELECT statement. You can also use a SELECT statement with the procedure call, although it is not strictly necessary.

SET result_var = (SELECT process_data());
SELECT $result_var;

Step 4: Remove unnecessary BEGIN/END Block. The original BEGIN/END block is redundant when using SET for variable assignment. It’s unnecessary complexity for this simple scenario.

Common Pitfalls & What to Check Next:

• Data Type Mismatch: Ensure the data type of your SQL variable (result_var in this case) matches the return type of your Python stored procedure (STRING). A mismatch can lead to implicit type conversion errors or unexpected results.
• Procedure Errors: If you still encounter errors, thoroughly check your Python stored procedure (process_data()) for any internal issues or errors preventing it from executing correctly or returning the expected value.
• User-Defined Functions (UDFs): For more complex scenarios involving multiple return values or more intricate logic, consider using a user-defined function (UDF) instead of a stored procedure. UDFs offer more flexibility in handling multiple output parameters.

Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!

[Ava89]

You can’t use EXECUTE IMMEDIATE with INTO to capture stored procedure return values in Snowflake. Use direct assignment with SET instead:

SET result_var = (SELECT process_data());

Or skip the SELECT wrapper:

SET result_var = process_data();

Ditch the BEGIN/END block - you don’t need it for simple variable assignments. Once you’ve set the variable, reference it with $result_var in other statements. This works great with Python stored procedures that return strings or numbers.