src/main/java/com/conveyal/gtfs/loader/Field.java
public String getColumnExpression(String prefix, boolean csvOutput) {
        return prefix != null ? String.format("%s%s", prefix, name) : name;
    }
public String getColumnExpression(String prefix, boolean csvOutput) {
        return prefix != null ? String.format("%s%s", prefix, name) : name;
    }
Get the expression used to select this column from the database based on the prefix.  The csvOutput parameter is
needed in overriden method implementations that have special ways of outputting certain fields.  The prefix
parameter is assumed to be either null or a string in the format: `schema.`