参考：https://www.imooc.com/learn/1281
语法格式:
SELECT 字段名 FROM 表名 WHERE 条件;
1.比较运算符
> 大于、< 小于、<= 小于等于、>= 大于等于、= 等于、<>不等于、!= 不等于
SELECT * FROM student WHERE mark >= 90;
SELECT * FROM student WHERE mark <= 85;
SELECT * FROM student WHERE sname = 'Jack';
SELECT * FROM student WHERE mark <> 86;
SELECT * FROM student WHERE sname != 'Bob';
Snipaste_2020-10-10_11-06-37.png
2.逻辑运算符
and 多个条件同时满足
or 多个条件其中一个满足
not 不满足
SELECT * FROM student WHERE mark >= 85 AND mark <= 95;
SELECT * FROM student WHERE mark <= 85 OR id >= 3;
SELECT * FROM student WHERE NOT mark <> 86;
Snipaste_2020-10-10_13-25-48.png
3.int关键字
SELECT 字段名 FROM 表名 WHERE 字段 in (数据1, 数据2...);
in里面的每个数据都会作为一次条件，只要满足条件的就会显示，括号里可以是SQL语句
SELECT * FROM student WHERE id in(1,3,5);
SELECT * FROM student WHERE id NOT in(1,3,5);
Snipaste_2020-10-10_13-29-03.png
4.范围查询
SELECT 字段名 FROM 表名 WHERE 字段 BETWEEN 值1 AND 值2;
包含值1和值2，值2>=值1，否则查不到
SELECT * FROM student WHERE mark BETWEEN 85 AND 95;
SELECT * FROM student WHERE mark BETWEEN 95 AND 85;
Snipaste_2020-10-10_13-51-52.png
5.模糊查询like
SELECT * FROM 表名 WHERE 字段名 LIKE '通配符字符串';
%: 表示0个或多个字符(任意个字符)
_: 表示一个字符
注意：不区分大小写
SELECT * FROM student WHERE sname LIKE 'R%';
SELECT * FROM student WHERE sname LIKE '%y';
SELECT * FROM student WHERE sname LIKE '%r%';
SELECT * FROM student WHERE sname LIKE 'R___'; --三个_
Snipaste_2020-10-10_14-12-06.png
