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coalesce Function

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coalesce Function

The coalesce function returns the first (left-most) non-null element from a given set.

Syntax

Alchemy
Copy
ret_val = coalesce(value_set);

Nomenclature

ret_val The first (left-most) non-null element in value_set
value_setA set of values to test

Example

The following example demonstrates the use of the coalesce function to select the most-specific known locale for a street (where the street is identified by id) using the lookup function (which returns null if a match is not made):

Alchemy
Copy
$my_region = coalesce(lookup(my_suburbs, %id), lookup(my_cities, %id), "Unknown"));

The above line of code is functionally equivalent to the following:

Alchemy
Copy
IF lookup(my_suburbs, %id) != NULL
  $my_region = lookup(my_suburbs, %id);

ELSE IF lookup(my_cities, %id) != NULL
  $my_region = lookup(my_cities, %id);

ELSE
  $my_region = "Unknown";