{
  "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"]
}