SINGULAR function

The SINGULAR function returns a Boolean value that indicates whether a list contains exactly one element.

Syntax

Read syntax diagramSkip visual syntax diagramSINGULAR(ListExpression)

If the list specified by ListExpression contains exactly one element, SINGULAR returns TRUE. If the list contains more or fewer elements, SINGULAR returns FALSE.

ListExpression is an expression that returns a list. All the following expressions, for example, return a list:
  • A LIST constructor
  • A field reference with the [] array indicator
  • Some SELECT expressions (not all return a list)

If you want to know only whether a list contains just one element or some other number, SINGULAR executes more quickly than an expression involving the CARDINALITY function (for example, CARDINALITY(ListExpression ) = 1).

A typical use of this function is to determine whether a field is unique.

Examples

-- Determine whether there is just one F1 field in the message.
-- Note that the [ ] are required
DECLARE Field1Unique BOOLEAN SINGULAR(OutputRoot.XMLNS.Data.Source.F1[]);
-- Determine whether there is just one field called F1 with the value 'F12'
-- in the message. Again note that the [ ] are required
DECLARE Field1F12Unique BOOLEAN
  SINGULAR(SELECT F.* FROM OutputRoot.XMLNS.Data.Source.F1[] AS F where F = 'F12');