ST_Z-PolarDB(PolarDB)-阿里云帮助中心

Returns the Z coordinate of a point geometry as a float.

Syntax

float ST_Z(geometry aPoint);

Parameter	Description
`aPoint`	The point geometry from which to extract the Z coordinate.

aPoint must be a point geometry. Passing any other geometry type returns NULL.
Returns NULL if the input is unavailable or invalid.
Preserves Z coordinates on 3D objects — the function does not strip or modify the Z value.

Return the Z coordinate of a 3D point:

SELECT ST_Z('POINT(0 1 2 3)'::geometry);
 st_z
------
    2
(1 row)

The input POINT(0 1 2 3) uses the WKT format where the third value (2) is the Z coordinate. ST_Z returns 2 as a float.