CREATE FUNCTION

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The CREATE FUNCTION statement creates a user-defined function.

Required privileges

• To create a function, a user must have CREATE privilege on the schema of the function. The user must also have privileges on all the objects referenced in the function body.
• To define a function with a user-defined type, a user must have USAGE privilege on the user-defined type.
• To resolve a function, a user must have at least the USAGE privilege on the schema of the function.
• To call a function, a user must have EXECUTE privilege on the function. By default, the user must also have privileges on all the objects referenced in the function body. However, a SECURITY DEFINER function executes with the privileges of the user that owns the function, not the user that calls it. A SECURITY INVOKER function executes with the privileges of the user that calls the function, thus matching the default behavior.

If you grant EXECUTE privilege as a default privilege at the database level, newly created functions inherit that privilege from the database.

Synopsis

Parameters

Example of a simple function

The following statement creates a function to compute the square of integers:

CREATE OR REPLACE FUNCTION sq(a INT) RETURNS INT AS 'SELECT a*a' LANGUAGE SQL;

The following statement invokes the sq function:

SELECT sq(2);

  sq
-----
  4
(1 row)

Examples of functions that reference tables

Setup

To follow along, run cockroach demo to start a temporary, in-memory cluster with the movr sample dataset preloaded:

$ cockroach demo

Create a function that references a table

The following statement defines a function that returns the total number of MovR application users.

CREATE OR REPLACE FUNCTION num_users() RETURNS INT AS 'SELECT count(*) FROM users' LANGUAGE SQL;

SELECT num_users();

  num_users
-------------
         50
(1 row)

Create a function that modifies a table

The following statement defines a function that updates the rules value for a specified row in promo_codes.

CREATE OR REPLACE FUNCTION update_code(
  code_name VARCHAR,
  new_rules JSONB
  ) 
  RETURNS promo_codes AS $$
    UPDATE promo_codes SET rules = new_rules
    WHERE code = code_name
    RETURNING *;
  $$ LANGUAGE SQL;

Given the promo_codes row:

            code           |                          description                           |    creation_time    |   expiration_time   |                    rules
---------------------------+----------------------------------------------------------------+---------------------+---------------------+-----------------------------------------------
  0_building_it_remember   | Door let Mrs manager buy model. Course rock training together. | 2019-01-09 03:04:05 | 2019-01-14 03:04:05 | {"type": "percent_discount", "value": "10%"}

SELECT update_code('0_building_it_remember', '{"type": "percent_discount", "value": "50%"}');

                                                                                          update_code
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  (0_building_it_remember,"Door let Mrs manager buy model. Course rock training together.","2019-01-09 03:04:05","2019-01-14 03:04:05","{""type"": ""percent_discount"", ""value"": ""50%""}")

Create a function that uses a WHERE clause

The following statement defines a function that returns the total revenue for rides taken in European cities.

CREATE OR REPLACE FUNCTION total_euro_revenue() RETURNS DECIMAL LANGUAGE SQL AS $$
  SELECT SUM(revenue) FROM rides WHERE city IN ('paris', 'rome', 'amsterdam')
$$;

SELECT total_euro_revenue();

  total_euro_revenue
----------------------
             8468.00

Create a function that returns a set of results

The following statement defines a function that returns information for all vehicles not in use. The SETOF clause specifies that the function should return each row as the query executes to completion.

CREATE OR REPLACE FUNCTION available_vehicles() RETURNS SETOF vehicles LANGUAGE SQL AS $$
  SELECT * FROM vehicles WHERE status = 'available'
$$;

SELECT city,current_location,type FROM available_vehicles();

      city      |      current_location       |    type
----------------+-----------------------------+-------------
  amsterdam     | 4102 Stout Flat Apt. 11     | skateboard
  boston        | 30226 Logan Branch Suite 76 | skateboard
  los angeles   | 25730 Crystal Terrace       | scooter
  paris         | 9429 Joseph Neck Suite 52   | skateboard
  san francisco | 43325 Jeffrey Wall Suite 26 | scooter
(5 rows)

Create a function that returns a RECORD type

The following function returns the information for the user that most recently completed a ride. The information is returned as a record, which takes the structure of the row that is retrieved by the selection query.

In the function subquery, the latest end_time timestamp is used to determine the most recently completed ride:

CREATE OR REPLACE FUNCTION last_rider() RETURNS RECORD LANGUAGE SQL AS $$
  SELECT * FROM users WHERE id = (
    SELECT rider_id FROM rides WHERE end_time = (SELECT max(end_time) FROM rides)
  )
$$;

SELECT last_rider();

                                                    last_rider
-------------------------------------------------------------------------------------------------------------------
  (147ae147-ae14-4b00-8000-000000000004,"new york","Isabel Clark DVM","98891 Timothy Cliffs Suite 39",4302568047)
(1 row)

Create a function that returns a table

The following function returns information for the last x users that recently completed a ride. The information is returned as a table, which is equivalent to a set of RECORD values. The rows are sorted in order of most recent ride.

The RETURNS TABLE clause specifies the column names to output: id, name, city, and end_time. A common table expression reads the most recent rides from the rides table.

CREATE OR REPLACE FUNCTION last_x_riders(x INT) RETURNS TABLE(id UUID, name VARCHAR, city VARCHAR, end_time TIMESTAMP) LANGUAGE SQL AS $$
  WITH recent_rides AS (
    SELECT rider_id, end_time FROM rides
    ORDER BY end_time DESC
  )
  SELECT u.id, u.name, u.city, r.end_time FROM users u, recent_rides r
  WHERE u.id = r.rider_id
  ORDER BY r.end_time DESC
  LIMIT x
$$;

SELECT * FROM last_x_riders(5);

                   id                  |       name       |     city      |      end_time
---------------------------------------+------------------+---------------+----------------------
  147ae147-ae14-4b00-8000-000000000004 | Isabel Clark DVM | new york      | 2019-01-04 14:04:05
  8f5c28f5-c28f-4000-8000-00000000001c | Patricia Sexton  | los angeles   | 2019-01-04 08:04:05
  75c28f5c-28f5-4400-8000-000000000017 | Andre Wilson     | san francisco | 2019-01-04 07:04:05
  00000000-0000-4000-8000-000000000000 | William Martin   | new york      | 2019-01-04 04:04:05
  d1eb851e-b851-4800-8000-000000000029 | Terry Reyes      | paris         | 2019-01-03 21:04:05
(5 rows)

Create a function that uses OUT and INOUT parameters

The following statement uses a combination of OUT and INOUT parameters to modify a provided value and output the result. An OUT parameter returns a value, while an INOUT parameter passes an input value and returns a value.

CREATE OR REPLACE FUNCTION double_triple(INOUT double INT, OUT triple INT) AS 
  $$
  BEGIN
    double := double * 2;
    triple := double * 3;
  END;
  $$ LANGUAGE PLpgSQL;

SELECT double_triple(1);

  double_triple
-----------------
  (2,6)

The CREATE FUNCTION statement does not need a RETURN statement because this is added implicitly for a function with OUT parameters:

SHOW CREATE FUNCTION double_triple;

  function_name |                             create_statement
----------------+---------------------------------------------------------------------------
  double_triple | CREATE FUNCTION public.double_triple(INOUT double INT8, OUT triple INT8)
                |     RETURNS RECORD
                |     VOLATILE
                |     NOT LEAKPROOF
                |     CALLED ON NULL INPUT
                |     LANGUAGE plpgsql
                |     AS $$
                |     BEGIN
                |     double := double * 2;
                |     triple := double * 3;
                |     END;
                | $$

Create a function that invokes a function

The following statement defines a function that invokes the double_triple example function.

CREATE OR REPLACE FUNCTION f(input_value INT)
  RETURNS RECORD 
  AS $$
  BEGIN
      RETURN double_triple(input_value);
  END;
  $$ LANGUAGE PLpgSQL;

SELECT f(1);

    f
---------
  (2,6)

Create a function that uses a loop

The following user-defined function returns the nth integer in the Fibonacci sequence.

It uses the PL/pgSQL LOOP syntax to iterate through a simple calculation, and RAISE EXCEPTION to return an error message if the specified n is negative.

CREATE FUNCTION fib(n int) RETURNS INT AS $$
    DECLARE
        tmp INT;
        a INT := 0;
        b INT := 1;
        i INT := 2;
    BEGIN
        IF n < 0 THEN
            RAISE EXCEPTION 'n must be non-negative';
        END IF;
        IF n = 0 THEN RETURN 0; END IF;
        IF n = 1 THEN RETURN 1; END IF;
        LOOP
            IF i > n THEN EXIT; END IF;
            tmp := a + b;
            a := b;
            b := tmp;
            i := i + 1;
        END LOOP;
        RETURN b;
    END
  $$ LANGUAGE PLpgSQL;

SELECT fib(8);

  fib
-------
   21

Create a trigger function

A trigger function is a function that is executed by a trigger. A trigger function must return type TRIGGER and is written in PL/pgSQL.

CREATE OR REPLACE FUNCTION change_name()
RETURNS TRIGGER AS $$
BEGIN
  NEW.name = 'Dear ' || (NEW).name;
  RETURN NEW;
END;
$$ LANGUAGE PLpgSQL;

The preceding example modifies a given name value and returns the NEW trigger variable because it is meant to be executed by a BEFORE trigger. For details, refer to Triggers.

Create a SECURITY DEFINER function

The following example defines a function using the SECURITY DEFINER clause. This causes the function to execute with the privileges of the function owner.

1. Create two roles:

   CREATE ROLE owner;
   CREATE ROLE invoker;
   

2. Grant a SELECT privilege on the user_promo_codes table to the owner role.

   GRANT SELECT ON TABLE user_promo_codes TO owner;
   

3. Set your role to owner.

   SET ROLE owner;
   

4. Create a simple SECURITY DEFINER function that reads the contents of user_promo_codes.

   CREATE OR REPLACE FUNCTION get_codes() 
     RETURNS SETOF RECORD 
     LANGUAGE SQL 
     SECURITY DEFINER
     AS $$
       SELECT * FROM user_promo_codes;
     $$;
   

5. Grant the EXECUTE privilege on the get_codes function to the invoker role.

   GRANT EXECUTE ON FUNCTION get_codes() TO invoker;
   

   Note:

   This step is not necessary if the function is defined on the public schema, for which roles automatically have the EXECUTE privilege.

6. Set your role to invoker.

   SET ROLE invoker;
   

7. invoker does not have the privileges to read the user_promo_codes table directly:

   SELECT * FROM user_promo_codes;
   

   ERROR: user invoker does not have SELECT privilege on relation user_promo_codes
   SQLSTATE: 42501
   

8. As invoker, call the get_codes function to read user_promo_codes, since SECURITY DEFINER is executed with the privileges of the owner role (i.e., SELECT on user_promo_codes).

   SELECT get_codes();
   

                                                    get_codes
   ------------------------------------------------------------------------------------------------------------
     ("new york",00000000-0000-4000-8000-000000000000,0_audience_thought_seven,"2019-01-02 03:04:05",10)
     ("new york",051eb851-eb85-4ec0-8000-000000000001,1_assume_its_leg,"2019-01-02 03:04:05.001",0)
     ("new york",0a3d70a3-d70a-4d80-8000-000000000002,2_popular_if_describe,"2019-01-02 03:04:05.002",16)
     ("new york",0f5c28f5-c28f-4c00-8000-000000000003,3_environmental_myself_add,"2019-01-02 03:04:05.003",4)
     ("new york",147ae147-ae14-4b00-8000-000000000004,4_rule_edge_career,"2019-01-02 03:04:05.004",13)
   (5 rows)
   

See also

• User-Defined Functions
• ALTER FUNCTION
• DROP FUNCTION
• SQL Statements
• Online Schema Changes