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{
"name": "z_min",
"type": "function",
"groups": ["GeometryGroup"],
"description": "Returns the minimum z coordinate of a geometry, or NULL if the geometry has no z value.",
"arguments": [{
"arg": "geometry",
"description": "a geometry with z coordinate"
}],
"examples": [{
"expression": "z_min( geom_from_wkt( 'POINT ( 0 0 1 )' ) )",
"returns": "1"
}, {
"expression": "z_min( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) )",
"returns": "1"
}, {
"expression": "z_min( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) )",
"returns": "-2"
}, {
"expression": "z_min( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )' ) )",
"returns": "-1"
}, {
"expression": "z_min( geom_from_wkt( 'POINT ( 0 0 )' ) )",
"returns": "NULL"
}],
"tags": ["coordinate", "minimum"]
}