ST_X

Return the X coordinate of a POINT geometry.

Category: geospatialReturns: DOUBLEDialect: Standard

Syntax

ST_X(point)

Description

## Overview Returns the X ordinate of a POINT geometry as a DOUBLE. For geographic data X corresponds to longitude in decimal degrees. The X value represents east/west position: negative values are west of the prime meridian, positive values are east. ST_X is the inverse of the first argument of ST_MAKE_POINT. Together with ST_Y it round-trips a POINT geometry back into its two numeric coordinates. ## When to use ST_X vs. alternatives - **ST_X** (this function): extract the X (longitude) coordinate from a POINT. - **ST_Y**: extract the Y (latitude) coordinate from a POINT. - **ST_AS_TEXT**: serialize the entire geometry as WKT when you need both coordinates and their layout. - **Direct column access**: if your table already stores lng and lat as separate DOUBLE columns, there is no need to build a POINT and then extract. ## Behavior - Returns a DOUBLE. - Works only on POINT geometries. LINESTRING, POLYGON, or multi-geometries raise an error or return NULL depending on runtime mode; use a different ST_ function to reduce them to a POINT first (for example the centroid). - Returns NULL if the input geometry is NULL. - The value is the raw X ordinate stored in the geometry; no CRS transformation is performed. - On an empty POINT, behavior is implementation-defined; prefer filtering out empty geometries explicitly. ## Input format - Accepts any POINT built with ST_MAKE_POINT, parsed with ST_GEOM_FROM_TEXT, or returned by other ST_ functions that produce a POINT. - The caller is responsible for tracking whether X means longitude, easting, or something else entirely based on the CRS of the input. ## Compatibility - Matches the OGC Simple Features ST_X semantics for 2D POINT geometries. - Returns the raw ordinate value with no unit conversion, matching other SQL engines that expose ST_X.

Parameters

Name	Type	Description
`point`		Specifies a POINT geometry whose X coordinate to extract. For geographic data X is longitude in decimal degrees. Non-POINT inputs raise an error or return NULL depending on runtime mode.

Examples

-- X is longitude for geographic data; expect -74.006.
SELECT ST_X(ST_MAKE_POINT(-74.0060, 40.7128)) AS lng;

-- WKT coordinate order is (x y), so the first number is X.
SELECT ST_X(ST_GEOM_FROM_TEXT('POINT(2.3522 48.8566)')) AS lng;

-- Denormalize a POINT column into lng/lat columns for downstream tooling.
SELECT id,
       ST_X(geom) AS lng,
       ST_Y(geom) AS lat
FROM geo.catalog.poi;

-- X > 0 selects everything east of longitude 0.
SELECT id
FROM geo.catalog.poi
WHERE ST_X(geom) > 0;

-- Reconstruct the original point from its coordinates.
SELECT ST_MAKE_POINT(ST_X(geom), ST_Y(geom)) AS geom2
FROM geo.catalog.poi;

-- A NULL geometry returns NULL.
SELECT ST_X(CAST(NULL AS GEOMETRY)) AS lng;

Pitfalls

X is longitude, not latitude. Calling ST_X and assigning the result to a column named 'lat' produces invisible but severe data corruption; verify orientation during ingest.
ST_X works only on POINT geometries. Feeding a LINESTRING or POLYGON raises an error in strict mode and returns NULL in lenient mode; extract a representative point first.
The function returns the raw ordinate value in the CRS of the geometry. A projected geometry returns easting (often in meters), not longitude; do not mix raw outputs from different coordinate systems.
Empty POINT geometries have implementation-defined behavior. Filter out empties before calling if NULLs or zeros would mask a data issue.
If the source column stores lng and lat separately, there is no benefit to building a POINT and calling ST_X afterward; use the numeric column directly.