SDO_TUNE.EXTENT

Format

SDO_TUNE.EXTENT_OF(
     table_name  IN VARCHAR2, 
     column_name IN VARCHAR2, 
     use_index   VARCHAR2 default 'TRUE' 
     ) RETURN SDO_GEOMETRY;

Description

Returns the minimum bounding rectangle (MBR) of all geometries in a layer.

Parameters

table_name: Spatial geometry table, or a view based on a spatial geometry table.
column_name: Geometry column for which the minimum bounding rectangle is to be returned.
use_index: The string TRUE (the default) causes the spatial index (if one exists) on the table to be used in the computations. The string FALSE causes any spatial index to be ignored. (See the Usage Notes for more information about this parameter.)

Usage Notes

The SDO_AGGR_MBR function, documented in Spatial Aggregate Functions, also returns the MBR of geometries. The SDO_TUNE.EXTENT_OF function has better performance than the SDO_AGGR_MBR function if a spatial index is defined on the geometry column; however, the SDO_TUNE.EXTENT_OF function is limited to two-dimensional geometries, whereas the SDO_AGGR_MBR function is not. In addition, the SDO_TUNE.EXTENT_OF function computes the extent for all geometries in a table; by contrast, the SDO_AGGR_MBR function can operate on subsets of rows.

If an R-tree spatial index is used, this function may return an approximate MBR that encloses the largest extent of data stored in the index, even if data was subsequently deleted.

The default value of TRUE for use_index is best in most cases, but in some cases you may want to specify FALSE. A spatial index can sometimes have the extent as larger than the actual data extent because DML operations might delete data around the edges, resulting in a smaller actual extent, although such deletions do not reduce the index extent. In such cases, if you want the actual data extent, specify use_index=>'FALSE'. Note, however, that specifying FALSE will have a significant negative impact on the performance of the function because it will require a full table scan.

Examples

The following example calculates the minimum bounding rectangle for the objects in the SHAPE column of the COLA_MARKETS table.

SELECT SDO_TUNE.EXTENT_OF('COLA_MARKETS', 'SHAPE') 
  FROM DUAL;

SDO_TUNE.EXTENT_OF('COLA_MARKETS','SHAPE')(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, 
--------------------------------------------------------------------------------
SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 3), SDO_ORDINATE_ARRAY(1, 1, 10, 11))