ST_MultiPoint
If the geometry-expression is of type ST_MultiPoint, returns the geometry-expression. If the geometry-expression is a geometry collection containing only points, returns a multipoint object containing the elements of the geometry-expression. If the geometry-expression is of type ST_Point then return a multi-point value containing one element, the geometry-expression. If the geometry-expression is the empty set, returns an empty set of type ST_MultiPoint. Otherwise, raises an exception condition.
The spatial reference system identifier of the result is the same as the spatial reference system of the geometry-expression.
If geometry-expression is already known to be an ST_MultiPoint value, it is more efficient to use TREAT( geometry-expression AS ST_MultiPoint ) than the ST_ToMultiPoint method.
Note
By default, ST_ToMultiPoint uses the original format for a geometry, if it is available. Otherwise, the internal format is
used. For more information about internal and original formats, see STORAGE FORMAT clause, CREATE SPATIAL REFERENCE SYSTEM statement.