PostGIS

ST_SRID — Returns the spatial reference identifier for a geometry.

+integer +ST_SRID(+`geometry `+g1`)`;

Returns the spatial reference identifier for the ST_Geometry as defined in spatial_ref_sys table. Section 4.5, “Spatial Reference Systems”

This method implements the OGC Simple Features Implementation Specification for SQL 1.1. s2.1.1.1

This method implements the SQL/MM specification. SQL-MM 3: 5.1.5

This method supports Circular Strings and Curves

Section 4.5, “Spatial Reference Systems”, ST_SetSRID, ST_Transform, ST_SRID, ST_SRID