四. MySQL 之 数据过滤

MySQL 数据过滤

1. 结合WHERE子句
   选出 kw = ‘投诉’ 并且 prob <= 0.15的行

  SELECT kw, prob FROM key_words WHERE kw = '投诉' AND prob <= 0.15;

2. OR操作符

SELECT kw, prob FROM key_words WHERE kw = '投诉' or prob >= 0.2

3. AND OR计算顺序问题
   SQL优先处理AND,后处理OR
   下面的例子中加括号与不加括号结果不一样

SELECT kw, prob FROM key_words WHERE kw='投诉' OR kw='影响' AND prob >= 0.2;

SELECT kw, prob FROM key_words WHERE (kw='投诉' OR kw='影响') AND prob >= 0.2;

4. IN操作符

SELECT kw, prob FROM key_words WHERE kw in ('投诉', '影响') ORDER BY prob DESC;
效果同
SELECT kw, prob FROM key_words WHERE kw='投诉' OR kw='影响' ORDER BY prob DESC;

说明：IN WHERE子句中用来指定要匹配值的清单的关键字，功能与OR
相当

5. NOT操作符-否定它之后所跟的任何条件
   用在WHERE子句中用来否定后跟条件的关键字

SELECT kw, prob FROM key_words WHERE kw NOT IN ('投诉', '影响') ORDER BY prob DESC;