ST_LineInterpolatePoint(ls, fractional_distance)

This function takes a LineString geometry and a fractional distance in
the range [0.0, 1.0] and returns the Point along the LineString at the
given fraction of the distance from its start point to its endpoint. It
can be used to answer questions such as which Point lies halfway along
the road described by the geometry argument.

The function is implemented for LineString geometries in all spatial
reference systems, both Cartesian and geographic.

If the fractional_distance argument is 1.0, the result may not be
exactly the last point of the LineString argument but a point close to
it due to numerical inaccuracies in approximate-value computations.

A related function, ST_LineInterpolatePoints(), takes similar arguments
but returns a MultiPoint consisting of Point values along the
LineString at each fraction of the distance from its start point to its
endpoint. For examples of both functions, see the
ST_LineInterpolatePoints() description.

ST_LineInterpolatePoint() handles its arguments as described in the
introduction to this section, with these exceptions:

o If the geometry argument is not a LineString, an
  ER_UNEXPECTED_GEOMETRY_TYPE
  (https://dev.mysql.com/doc/mysql-errors/8.0/en/server-error-reference
  .html#error_er_unexpected_geometry_type) error occurs.

o If the fractional distance argument is outside the range [0.0, 1.0],
  an ER_DATA_OUT_OF_RANGE
  (https://dev.mysql.com/doc/mysql-errors/8.0/en/server-error-reference
  .html#error_er_data_out_of_range) error occurs.

URL: https://dev.mysql.com/doc/refman/8.0/en/spatial-operator-functions.html

