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Geometry 2D functions
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DOUBLE ST_YMax(GEOMETRY geom);
Returns the maximum y-value of geom.
geom
SELECT ST_YMax('LINESTRING(1 2 3, 4 5 6)'); -- Answer: 5.0
ST_XMin, ST_XMax, ST_YMin, ST_ZMax, ST_ZMin
ST_XMin
ST_XMax
ST_YMin
ST_ZMax
ST_ZMin
Source code