Explanation/Reference:
SDO_within_distance determines if two geometries are within a specified distance from one another.
Returns
The expression SDO_WITHIN_DISTANCE(arg1, arg2, arg3) = 'TRUE' evaluates to TRUE for object pairs that are within the specified distance, and FALSE otherwise.
Format: SDO_WITHIN_DISTANCE(geometry1, aGeom, params);
The operator must always be used in a WHERE clause and the condition that includes the operator should be an expression of the form:
SDO_WITHIN_DISTANCE(arg1, arg2, 'distance = <some_dist_val>') = 'TRUE'
Note: Parameters:
geometry1
Specifies a geometry column in a table. The column has the set of geometry objects that will be operated on to determine if they are within the specified distance of the given object (aGeom). The column must be spatially indexed. Data type is SDO_GEOMETRY.
aGeom
Specifies the object to be checked for distance against the geometry objects in geometry1. Specify either a geometry from a table (using a bind variable) or a transient instance of a geometry (using the SDO_GEOMETRY constructor). Data type is SDO_GEOMETRY.
Params
A quoted string containing one or more keywords (with values) that determine the behavior of the operator.
The remaining items (distance, max_resolution, min_resolution, querytype, and unit) are potential keywords for the params parameter. Data type is VARCHAR2.
Distance
Specifies the distance value. If a coordinate system is associated with the geometry, the distance unit is assumed to be the unit associated with the coordinate system. This is a required keyword. Data type is NUMBER.
Unit
Specifies the unit of measurement: a quoted string with unit= and an SDO_UNIT value from the MDSYS.SDO_DIST_UNITS table (for example, 'unit=KM'). Data type is NUMBER. Default = unit of measurement associated with the data. For geodetic data, the default is meters.
References: https://docs.oracle.com/cd/B28359_01/appdev.111/b28400/sdo_operat.htm#SPATL1041