Custom data metric functions¶

Create a custom DMF¶

The following examples demonstrate how to use the CREATE DATA METRIC FUNCTION command to create a custom DMF.

Example: User-defined DMF with single table argument

Create a DMF that calls the COUNT function to return the total number of rows that have positive numbers in three columns of the table:

CREATE OR REPLACE DATA METRIC FUNCTION governance.dmfs.count_positive_numbers(
  arg_t TABLE(
    arg_c1 NUMBER,
    arg_c2 NUMBER,
    arg_c3 NUMBER
  )
)
RETURNS NUMBER
AS
$$
  SELECT
    COUNT(*)
  FROM arg_t
  WHERE
    arg_c1>0
    AND arg_c2>0
    AND arg_c3>0
$$;

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Example: Using multiple table arguments to perform referential checks

A user-defined DMF can have more than one argument that accepts a table. When you add the DMF to a table, that table is used as the first argument. If there is an additional argument that accepts a table, you must also specify the fully qualified name of the second table. This capability simplifies referential integrity, matching and comparison, or conditional checking across different datasets.

Suppose you want to validate referential integrity as defined by a primary key/foreign key relationship. In this case, you can create a DMF to validate that all records in a source table have corresponding records in the referenced table. The following user-defined DMF returns the number of records where the value of a column in one table does not have a corresponding value in the column of another table:

CREATE OR REPLACE DATA METRIC FUNCTION governance.dmfs.referential_check(
  arg_t1 TABLE (arg_c1 INT), arg_t2 TABLE (arg_c2 INT))
RETURNS NUMBER AS
 'SELECT COUNT(*) FROM arg_t1
  WHERE arg_c1 NOT IN (SELECT arg_c2 FROM arg_t2)';

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Now suppose you want to check whether every order, as identified by its sp_id, in the salesorders table maps back to an sp_id in the salespeople table. You can add the DMF to the salesorders table while specifying the salespeople table as the other table argument.

ALTER TABLE salesorders
  ADD DATA METRIC FUNCTION governance.dmfs.referential_check
    ON (sp_id, TABLE (my_db.sch1.salespeople(sp_id)));

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The output returns the number of rows in the salesorders table that have a value in the sp_id column that doesn’t appear in the sp_id column of the salespeople table. A value greater than 0 indicates that there are sp_id values in salesorders that don’t map to records in salespeople.

Secure the custom DMF¶

You can use the ALTER FUNCTION command to make a DMF secure. For more information about what it means for a function to be secure, see Protecting Sensitive Information with Secure UDFs and Stored Procedures.

ALTER FUNCTION governance.dmfs.count_positive_numbers(
 TABLE(
   NUMBER,
   NUMBER,
   NUMBER
))
SET SECURE;

View the properties of a DMF¶

Describe the DMF to view its properties:

DESC FUNCTION governance.dmfs.count_positive_numbers(
  TABLE(
    NUMBER, NUMBER, NUMBER
  )
);

+-----------+---------------------------------------------------------------------+
| property  | value                                                               |
+-----------+---------------------------------------------------------------------+
| signature | (ARG_T TABLE(ARG_C1 NUMBER, ARG_C2 NUMBER, ARG_C3 NUMBER))          |
| returns   | NUMBER(38,0)                                                        |
| language  | SQL                                                                 |
| body      | SELECT COUNT(*) FROM arg_t WHERE arg_c1>0 AND arg_c2>0 AND arg_c3>0 |
+-----------+---------------------------------------------------------------------+

Set a tag on a custom DMF¶

Use the ALTER FUNCTION command to set a tag on a DMF:

ALTER FUNCTION governance.dmfs.count_positive_numbers(
  TABLE(NUMBER, NUMBER, NUMBER))
  SET TAG governance.tags.quality = 'counts';

Drop a custom DMF¶

You can use the DROP FUNCTION command to remove a custom data metric function from the system.

Drop a custom DMF from the system:

DROP FUNCTION governance.dmfs.count_positive_numbers(
  TABLE(
    NUMBER, NUMBER, NUMBER
  )
);