PostGIS ST_Buffer a polyline?

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I am trying to run a buffer around a polyline (geography). My first attempt below (based on ST_Buffer documentation:

SELECT ST_Buffer(ST_Geomfromtext(i30.geog),10,'endcap=round join=round');gives an error:

missing FROM-clause entry for table "i30"ST_Geomfromtext(**^here**i30.geog)

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