code: private void executeDropIndex(Tree statement) throws TException, SchemaDisagreementException, InvalidRequestException, NotFoundException
      {
          if (!CliMain.isConnected() || !hasKeySpace())
              return;
  
          // getColumnFamily will check if CF exists for us
          String columnFamily = CliCompiler.getColumnFamily(statement, currentCfDefs());
          String rawColumName = CliUtils.unescapeSQLString(statement.getChild(1).getText());
  
          CfDef cfDef = getCfDef(columnFamily);
  
          ByteBuffer columnName = columnNameAsBytes(rawColumName, cfDef);
  
          boolean foundColumn = false;
  
          for (ColumnDef column : cfDef.getColumn_metadata())
          {
              if (column.name.equals(columnName))
              {
                  foundColumn = true;
  
                  if (column.getIndex_type() == null)
                      throw new RuntimeException(String.format("Column '%s' does not have an index.", rawColumName));
  
                  column.setIndex_name(null);
                  column.setIndex_type(null);
              }
          }
  
          if (!foundColumn)
              throw new RuntimeException(String.format("Column '%s' definition was not found in ColumnFamily '%s'.",
                                                       rawColumName,
                                                       columnFamily));
  
          String mySchemaVersion = thriftClient.system_update_column_family(cfDef);
          sessionState.out.println(mySchemaVersion);
          keyspacesMap.put(keySpace, thriftClient.describe_keyspace(keySpace));
      }
docs: DROP INDEX ON <CF>.<COLUMN>