You can instantiate a user-defined type to define a constructor as follows:

NEW type-name( argument-list)

For example, a query could contain the following to instantiate two ST_Point values:

SELECT NEW ST_Point(), NEW ST_Point(3,4)

SQL Anywhere matches argument-list against defined constructors using the normal overload resolution rules. An error is returned in the following situations:

See also:

• Accessing and manipulating spatial data
• ST_Point type

User defined types can have instance methods defined. Instance methods are invoked on a value of the type as follows:

value-expression.method-name( argument-list )

For example, the following selects the X coordinate of the myTable.centerpoint column:

SELECT centerpoint.ST_X() FROM myTable;

Note that if there was a user ID called centerpoint, the database server would find the construct centerpoint.ST_X() to be ambiguous. This is because the statement could mean "call the user-defined function ST_X owned by user centerpoint"--the incorrect intention of the statement--or it could mean "call the ST_X method on the myTable.centerpoint column" (the correct meaning). The database server resolves such ambiguity by first performing a case-insensitive search for a user named centerpoint. If a user named centerpoint is found, the database server proceeds as though a user-defined function called ST_X and owned by user centerpoint is being called. If no user called centerpoint is found, the database server treats the construct as a method call and calls the ST_X method on the myTable.centerpoint column.

An instance method invocation gives an error in the following cases:

See also:

• ST_X() method for type ST_Point

In addition to instance methods, the ANSI/SQL standard allows user-defined types to have static methods associated with them. These are invoked using the following syntax:

type-name::method-name( argument-list )

For example, the following instantiates an ST_Point by parsing text:

SELECT ST_Geometry::ST_GeomFromText('POINT( 5 6 )')

A static method invocation gives an error in the following cases:

See also:

• ST_Point type
• ST_GeomFromText method for type ST_Geometry

As an extension to ANSI/SQL, SQL Anywhere supports static methods that implement user-defined aggregates. For example:

SELECT ST_Geometry::ST_AsSVGAggr(T.geo) FROM table T

All of the overloads for a static method must be aggregate or none of them may be aggregate.

A static aggregate method invocation gives an error in the following cases:

See also:

• ST_AsSVGAggr method for type ST_Geometry

The ANSI/SQL standard defines type predicates that allow a statement to examine the dynamic type of a value. The syntax is as follows:

value  IS [ NOT ] OF ( [ ONLY ] type-name,...)

If value is NULL, the predicate returns UNKNOWN. Otherwise, the dynamic type of value is compared to each of the elements in the type-name list. If ONLY is specified, there is a match if the dynamic type is exactly the specified type. Otherwise, there is a match if the dynamic type is the specified type or any derived type (sub-type).

If the dynamic type of value matches one of the elements in the list, TRUE is returned, otherwise FALSE.

For example, the following returns T:

SELECT IF DT.x IS OF ( ST_Point ) THEN 'T' ENDIF
FROM ( SELECT ST_Geometry::ST_GeomFromText('POINT(5 6)') x ) DT

See also:

• Search conditions
• ST_Point type
• ST_GeomFromText method for type ST_Geometry

The ANSI/SQL standard defines a sub-type treatment expression that allows a cast from a base type to a sub-type (derived type). The syntax is as follows:

TREAT( value-expression AS target-subtype )

The following example casts ST_Geometry to sub-type ST_Point:

SELECT TREAT( DT.x AS ST_Point ) 
FROM ( SELECT ST_Geometry::ST_GeomFromText('POINT(5 6)') x ) DT

If no error condition is raised, the result is the value-expression with declared type of target-subtype.

The sub-type treatment expression gives an error in the following cases:

See also:

• TREAT function [Data type conversion]
• ST_Point type
• ST_GeomFromText method for type ST_Geometry