Calling Functions

Calling Functions

Using Positional Notation

Using Named Notation

Using Mixed Notation

Tacnode allows functions that have named parameters to be called using either positional or named notation. Named notation is especially useful for functions that have a large number of parameters, since it makes the associations between parameters and actual arguments more explicit and reliable. In positional notation, a function call is written with its argument values in the same order as they are defined in the function declaration. In named notation, the arguments are matched to the function parameters by name and can be written in any order. For each notation, also consider the effect of function argument types, documented in Section 9.3.

In either notation, parameters that have default values given in the function declaration need not be written in the call at all. But this is particularly useful in named notation, since any combination of parameters can be omitted; while in positional notation parameters can only be omitted from right to left.

Tacnode also supports mixed notation, which combines positional and named notation. In this case, positional parameters are written first and named parameters appear after them.

The following examples will illustrate the usage of all three notations, using the following function definition:

CREATE FUNCTION concat_lower_or_upper(a text, b text, uppercase boolean DEFAULT false)
RETURNS text
AS
$$
 SELECT CASE
        WHEN $3 THEN UPPER($1 || ' ' || $2)
        ELSE LOWER($1 || ' ' || $2)
        END;
$$
LANGUAGE SQL IMMUTABLE STRICT;

Function concat_lower_or_upper has two mandatory parameters, a and b. Additionally there is one optional parameter uppercase which defaults to false. The a and b inputs will be concatenated, and forced to either upper or lower case depending on the uppercase parameter. The remaining details of this function definition are not important here .

SELECT concat_lower_or_upper('Hello', 'World', true);
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)

SELECT concat_lower_or_upper('Hello', 'World');
 concat_lower_or_upper 
-----------------------
 hello world
(1 row)

SELECT concat_lower_or_upper(a => 'Hello', b => 'World');
 concat_lower_or_upper 
-----------------------
 hello world
(1 row)

SELECT concat_lower_or_upper(a => 'Hello', b => 'World', uppercase => true);
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)
 
SELECT concat_lower_or_upper(a => 'Hello', uppercase => true, b => 'World');
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)

SELECT concat_lower_or_upper(a := 'Hello', uppercase := true, b := 'World');
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)

SELECT concat_lower_or_upper('Hello', 'World', uppercase => true);
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)