I have a table already in BQ that is populated with data. I want to rename the headings (update the schema) of the table. I\'m using command line tool
Presuming it\'
As Mosha says, renaming columns is not supported via API, but you could run a query that scans the whole table and overwrites it.
bq query --nouse_legacy_sql \
--destination_table p:d.table \
--replace \
'SELECT * EXCEPT(col1,col2), col1 AS newcol1, col2 AS newcol2 FROM `p.d.table`'
Warning: This overwrites the table. But that's what you wanted anyways.