UDF CALL

Translation reference for User-defined function (UDF) Call

Description

As is widely acknowledged, non-scalar user-defined functions (UDFs) in Oracle are converted into Snowflake stored procedures to accommodate more intricate functionalities.

This transformation also alters the way the function is invoked, transitioning from a traditional function call to a stored procedure call.

For additional details regarding the invocation of stored procedures, refer to the documentation accessible here: PROCEDURE CALL.

Sample Source Patterns

Consider the next function and tables for the examples below.

Oracle

CREATE OR REPLACE FUNCTION sum_to_varchar_function(p_number1 IN NUMBER, p_number2 IN NUMBER)
RETURN VARCHAR
IS
    result VARCHAR(100);
BEGIN
    result := TO_CHAR(p_number1 + p_number2);
    RETURN result;
END sum_to_varchar_function;

CREATE TABLE example_table (
    id NUMBER,
    column1 NUMBER
);
INSERT INTO example_table VALUES (1, 15);

CREATE TABLE result_table (
    id NUMBER,
    result_col VARCHAR(100)
);

Snowflake

CREATE OR REPLACE PROCEDURE sum_to_varchar_function(p_number1 NUMBER(38, 18), p_number2 NUMBER(38, 18))
RETURNS VARCHAR
LANGUAGE SQL
EXECUTE AS CALLER
AS
$$
    DECLARE
        result VARCHAR(100);
    BEGIN
        result := TO_CHAR(:p_number1 + :p_number2);
        RETURN :result;
    END;
$$;

CREATE OR REPLACE TABLE example_table (
    id NUMBER(38, 18),
    column1 NUMBER(38, 18)
);

INSERT INTO example_table VALUES (1, 15);

CREATE OR REPLACE TABLE result_table (
    id NUMBER(38, 18),
    result_col VARCHAR(100)
);

UDF Call

Oracle

Query

CREATE OR REPLACE PROCEDURE procedure_calling_function(param1 IN NUMBER)
IS
    result_value VARCHAR(200);
BEGIN 
    result_value := sum_to_varchar_function(3, param1);
    INSERT INTO result_table VALUES (1, result_value);
END;

BEGIN
    procedure_calling_function(5);
END;

Result

ID	RESULT_COL
1	8

Snowflake Scripting

Query

CREATE OR REPLACE PROCEDURE procedure_calling_function (param1 NUMBER(38, 18))
RETURNS VARCHAR
LANGUAGE SQL
EXECUTE AS CALLER
AS
$$
DECLARE
    result_value VARCHAR(200);
BEGIN
    LET sum_to_varchar_function_TEMP_1 VARCHAR;
    sum_to_varchar_function_TEMP_1 := (CALL sum_to_varchar_function(3, :param1));
    result_value := :sum_to_varchar_function_TEMP_1;
    INSERT INTO result_table VALUES (1, :result_value);
END;
$$;

CALL procedure_calling_function(5);

Result

ID	RESULT_COL
1	8

UDF Call within a query

When a function call is embedded within a query, the invocation process becomes more intricate due to Snowflake's limitation of not being able to call procedures directly within queries. To overcome this limitation, the procedure invocation is moved outside the query, and the result is assigned to a variable. This variable is then referenced within the query, thereby achieving functional equivalence. This approach allows for the execution of more complex behaviors within Snowflake queries while adhering to the procedural constraints.

Oracle

Query

CREATE OR REPLACE PROCEDURE procedure_calling_function(param1 IN NUMBER)
IS
    result_value VARCHAR(200);
    result_value2 VARCHAR(200);
BEGIN 
    SELECT
        sum_to_varchar_function(1, param1) AS result_column,
        sum_to_varchar_function(2, param1) AS result_column2
    INTO result_value, result_value2
    FROM example_table ext;

    INSERT INTO result_table VALUES (1, result_value);
    INSERT INTO result_table VALUES (2, result_value2);
END;

BEGIN
    procedure_calling_function(5);
END;

Result

ID	RESULT_COL
1	6
2       7

Snowflake Scripting

Query

CREATE OR REPLACE PROCEDURE procedure_calling_function (param1 NUMBER(38, 18))
RETURNS VARCHAR
LANGUAGE SQL
EXECUTE AS CALLER
AS
$$
DECLARE
    result_value VARCHAR(200);
    result_value2 VARCHAR(200);
BEGIN
    LET sum_to_varchar_function_TEMP_1 VARCHAR;
    sum_to_varchar_function_TEMP_1 := (CALL sum_to_varchar_function(1, :param1));
    LET sum_to_varchar_function_TEMP_2 VARCHAR;
    sum_to_varchar_function_TEMP_2 := (CALL sum_to_varchar_function(2, :param1));

    SELECT
        :sum_to_varchar_function_TEMP_1 AS result_column,
        :sum_to_varchar_function_TEMP_2 AS result_column2
    INTO :result_value, :result_value2
    FROM example_table ext;

    INSERT INTO result_table VALUES (1, :result_value);
    INSERT INTO result_table VALUES (2, :result_value2);
END;
$$;

CALL procedure_calling_function(5);

Result

ID	RESULT_COL
1	6
2       7

Known Issues

1. Unsupported Usage of UDFs in Queries with Query Dependencies

When calling User-Defined Functions (UDFs) within queries with query dependencies, scenarios involving embedded functions with columns as arguments are not supported. This limitation arises because the column values cannot be accessed from outside the query. Examples of unsupported scenarios include:

BEGIN
    SELECT
        sum_to_varchar_function(ext.col1, ext.col2) -- columns as arguments not supported
    INTO
        result_value
    FROM example_table ext;
END;

The supported scenarios include function calls with other types of arguments such as literal values, external variables, or parameters. For instance:

BEGIN
    SELECT
        sum_to_varchar_function(100, param1)
    INTO
        result_value
    FROM example_table ext;
END;

In the supported scenarios, the function can effectively be migrated.

Related EWIs

1. SSC-EWI-0068: User defined function was transformed to a Snowflake procedure.