Returns the geometry which represents the geometric parts og geom1 and geom2 that do not intersect. It is called symmetric because ST_SymDifference(geom1,geom2) = ST_SymDifference(geom2,geom1). It can be understand as: ST_Union(geom1,geom2) - ST_Intersection(geom1,geom2).
 

1 geo.symDifference

<geo.symDifference ora_tol='ora_tol'>
    <geom1> *
        <geom1 /> *
    </geom1>
    <geom2> *
        <geom2 /> *
    </geom2>
</geo.symDifference>
Example
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<select>
    <columns>
       <geo.difference ora_tol=''>
            <geom1>geometry_col_1</geom1>
            <geom2>geometry_col_2</geom2>
       </geo.difference>
    </columns>
    <from table='buildings' alias='a' >
    </from>
    <where>
        a.name = 'MACBA'
    </where>
</select>