ST_LongestLine

Introduction: Returns the LineString geometry representing the maximum distance between any two points from the input geometries.

Format: ST_LongestLine(geom1: Geometry, geom2: Geometry)

SQL Example:

SELECT ST_LongestLine(
        ST_GeomFromText("POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))"),
        ST_GeomFromText("POLYGON ((10 20, 30 30, 40 20, 30 10, 10 20))")
)

Output:

LINESTRING (40 40, 10 20)

Output:

+------------------------------------------------------------------------------------------------+
|Substring                                                                                       |
+------------------------------------------------------------------------------------------------+
|LINESTRING (69.28469348539744 94.28469348539744, 100 125, 111.70035626068274 140.21046313888758)|
+------------------------------------------------------------------------------------------------+