@Override
    public Q addJoinFlag(String flag) {
        return addJoinFlag(flag, JoinFlag.Position.BEFORE_TARGET);
    }
Add the given String literal as a join flag to the last added join with the position
BEFORE_TARGET

@param flag join flag
@return the current object
querydsl-sql/src/main/java/com/querydsl/sql/ProjectableSQLQuery.java