简单搜索条件
SELECT number, name, id_number major FROM student_info WHERE name = '狗哥';
WHERE子句，用于匹配条件，后面接运算符表达式，可用的运算符有几下：
| 运算符 | 示例 | 描述 |
|---|---|---|
| = | a = b | a等于b |
| <=> | a <=> b | a等于b(NULL值安全) |
| <>或!= | a <> b | a不等于b |
| < | a < b | a小于b |
| <= | a <= b | a小于或等于b |
| > | a > b | a大于b |
| >= | a >= b | a大于或等于b |
| BETWEEN | a BETWEEN b AND c | a的值必须满足 b<=a<=c |
| NOT BETWEEN | a NOT BETWEEN b AND c | a的值必须不满足b<=a<=c |