ConvexHullAggregate (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns a convex hull for a given set of geometry objects.
Syntax
ConvexHullAggregate ( geometry_operand )
Arguments
geometry_operand
Is a geometry type table column that represents a set of geometry objects.
Return Types
SQL Server return type: geometry
Exception
Throws a FormatException when there are input values that are not valid. See STIsValid (geometry Data Type)
Remarks
Method returns null when the input is empty or the input has different SRIDs. See Spatial Reference Identifiers (SRIDs)
Method ignores null inputs.
Note
Method returns null if all inputted values are null.
Examples
The following example returns a convex hull of the set of geometry objects in a table variable column.
-- Setup table variable for ConvexHullAggregate example
DECLARE @Geom TABLE
(
shape geometry,
shapeType nvarchar(50)
)
INSERT INTO @Geom(shape,shapeType) VALUES('CURVEPOLYGON(CIRCULARSTRING(2 3, 4 1, 6 3, 4 5, 2 3))', 'Circle'),
('POLYGON((1 1, 4 1, 4 5, 1 5, 1 1))', 'Rectangle');
-- Perform ConvexHullAggregate on @Geom.shape column
SELECT geometry::ConvexHullAggregate(shape).ToString()
FROM @Geom;