MySQL没有split函数的替代方法

mysql的函数没有split，只能自己取字符串的index。

select  diff_range,
       CAST(
            if(
                LOCATE("-", diff_range)>0,
                substring(
                    diff_range, 1, LOCATE("-", diff_range)
                ) ,
                diff_range
            )
            as SIGNED  INTEGER
       )   a
  from test
where `ds` = "20180110"

结果如下

diff_range	a
1	1
2	2
3-6	3
7-15	7
16-30	16
31-100	31
101-200	101