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MSC-PG0027

FOUND could have a different behavior in Snowflake in some scenarios.

This is a deprecated version of the SnowConvert documentation, please visit the official site HERE.

Severity

Low

Description

The FOUND property in PostgreSQL is a property based on the last executed query, it can be affected by some statements such as INSERT, UPDATE, DELETE, MERGE, SELECT INTO, PERFORM, FETCH and FOR loops. To read more details about this property, this is PostgreSQL documentation.

In Snowflake there is not a direct translation for this property, for the following scenarios:

  • INSERT

  • UPDATE

  • DELETE

  • MERGE

The converted code will be SQLFOUND Snowflake property (Here is the documentation) since it behaves like the PostgreSQL FOUND property.

For the other cases such as:

  • SELECT INTO

  • PERFORM

  • FETCH

The converted code will be a custom UDF (IS_FOUND_UDF) that behaves like the PostgreSQL FOUND property.

This happens because SQLFOUND changes its value only when at least one row is affected by the last executed query, if the last query does not change any row, it does not change.

While the IS_FOUND_UDF only works for statements that returns rows, if no row is returned it, it will return FALSE.

SQLFOUND Example

INSERT INTO SampleTable (SampleColumn1)
VALUES ('SampleValue0.1');

The last query affects a table, so the SQLFOUND is the closest to the PostgreSQL functionality.

IS_FOUND_UDF Example

SELECT SampleColumn FROM SampleTable;

The last query will return a row but does not change anything, so the IS_FOUND_UDF() is the closest to the PostgreSQL functionality.

IS_FOUND_UDF Source Code

CREATE OR REPLACE FUNCTION IS_FOUND_UDF() 
RETURNS BOOLEAN
LANGUAGE SQL
IMMUTABLE
AS
$$
    SELECT (COUNT(*) != 0) FROM TABLE(RESULT_SCAN(LAST_QUERY_ID()));
$$;

Code Example

Insert Statement:

-- Found property used with INSERT statement.
CREATE OR REPLACE FUNCTION FoundUsingInsertFunction()
RETURNS BOOLEAN
AS
$$
  BEGIN
    INSERT INTO SampleTable (SampleColumn1)
    VALUES ('SampleValue0.1');
    RETURN FOUND;
  END;
$$
LANGUAGE plpgsql;

Update Statement:

-- Found property used with UPDATE statement.
CREATE OR REPLACE FUNCTION FoundUsingUpdateFunction()
RETURNS BOOLEAN
AS
$$
    BEGIN
        UPDATE SampleTable 
        SET SampleColumn1 = 'SampleValue0.1' 
        WHERE SampleColumn1 = 'SampleValue0.1';
        RETURN FOUND;
    END;
$$
LANGUAGE plpgsql;

Delete Statement:

-- Found property used with DELETE statement.
CREATE OR REPLACE FUNCTION FoundUsingDeleteFunction()
RETURNS BOOLEAN
AS
$$
    BEGIN
        DELETE FROM SampleTable 
        WHERE SampleColumn1 = 'SampleValue0.1';
        RETURN FOUND;
    END;
$$
LANGUAGE plpgsql;

Merge Statement:

-- Found property used with MERGE statement.
CREATE OR REPLACE FUNCTION FoundUsingMergeFunction()
RETURNS BOOLEAN
AS
$$
    BEGIN
        MERGE INTO SampleTableB B
        USING (SELECT * FROM SampleTableA) A
        ON B.SampleColumn1 = A.SampleColumn2
        WHEN MATCHED THEN DELETE;
        RETURN FOUND;
    END;
$$
LANGUAGE plpgsql;

Select Into Statement

-- Found property used with SELECT INTO statement.
CREATE OR REPLACE FUNCTION FoundUsingSelectIntoFunction()
RETURNS BOOLEAN
AS
$$
    DECLARE 
        SampleNumber INTEGER;
    BEGIN
        SELECT 1 INTO SampleNumber;
        RETURN FOUND;
    END;
$$
LANGUAGE plpgsql;

Perform Statement:

-- Found property used with PERFORM statement.
CREATE OR REPLACE FUNCTION FoundUsingPerformFunction()
RETURNS BOOLEAN
AS
$$
    BEGIN
        PERFORM 1;
        RETURN FOUND;
    END;
$$
LANGUAGE plpgsql;

Fetch Statement:

-- Found property used with FETCH statement.
CREATE OR REPLACE FUNCTION FoundUsingFetchFunction ()
RETURNS BOOLEAN
AS
$$
    DECLARE
        SampleRow VARCHAR;
        SampleCursor CURSOR FOR SELECT EmptyColumn FROM EmptyTable;
    BEGIN
        OPEN SampleCursor;
        FETCH SampleCursor;
        CLOSE SampleCursor;
        RETURN FOUND;
    END;
$$
LANGUAGE plpgsql;

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