ST_LineFromText — Makes a Geometry from WKT representation with the given SRID. If SRID is not given, it defaults to 0.
geometry ST_LineFromText(text  WKT);
geometry ST_LineFromText(text  WKT, integer  srid);
Makes a Geometry from WKT with the given SRID. If SRID is not given, it defaults to 0. If WKT passed in is not a LINESTRING, then null is returned.
                 
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                 OGC SPEC 3.2.6.2 - option SRID is from the conformance suite.  | 
            
                 
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                 If you know all your geometries are LINESTRINGS, its more efficient to just use ST_GeomFromText. This just calls ST_GeomFromText and adds additional validation that it returns a linestring.  | 
            
            
            This method implements the OGC Simple Features
            Implementation Specification for SQL 1.1.
         s3.2.6.2
            
            This method implements the SQL/MM specification.
         SQL-MM 3: 7.2.8
SELECT ST_LineFromText('LINESTRING(1 2, 3 4)') AS aline, ST_LineFromText('POINT(1 2)') AS null_return;
aline                            | null_return
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010200000002000000000000000000F ... | t