BETWEEN 用以查询确定范围的值，这些值可以是数字，文本或日期 。
BETWEEN 运算符是闭区间的：包括开始 和 结束值 。
not between 则是不包含前后边界的
!=’’ 会过滤掉值为 null 的数据.
The reason is simple: nulls are neither equal, nor not equal, to anything. This makes sense when you consider that null means “unknown”, and the truth of a comparison to an unknown value is also unknown.
The corollary is that:
null = null is not true null = some_value is not true null != some_value is not true The two special comparisons IS NULL and IS NOT NULL exist to deal with testing if a column is, or is not, null. No other comparisons to null can be true.