确实就是为了判断方便 比如
select * from 订单
where 1 = 1
${if(len(货主地区) == 0,"","and 货主地区 = '" + 货主地区 + "'")}
${if(len(订单ID) == 0,"","and 订单ID = '" + 货主地区 + "'")}
等效于
select * from 订单
${if(len(货主地区) == 0,""," WHERE 货主地区 = '" + 货主地区 + "'")}
${if(len(订单ID) == 0,"",if(len(货主地区) == 0," WHERE 订单ID = '" + 货主地区 + "'"," AND订单ID = '" + 货主地区 + "'"))}
明显第二种方法就复杂多了 太容易出错