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@ -432,11 +432,11 @@ FROM |
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student_info; |
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student_info; |
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``` |
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``` |
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### 7.4 查询所有列 |
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## 7.4 查询所有列 |
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- 方法:`SELECT * FROM student_info;` |
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- 方法:`SELECT * FROM student_info;` |
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### 7.5 查询结果去重 |
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## 7.5 查询结果去重 |
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- 方法:`SELECT DISTINCT department[, 列名] FROM student_info` |
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- 方法:`SELECT DISTINCT department[, 列名] FROM student_info` |
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@ -445,18 +445,72 @@ SELECT DISTINCT department FROM student_info; |
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SELECT DISTINCT department, major FROM student_info; |
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SELECT DISTINCT department, major FROM student_info; |
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``` |
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``` |
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### 7.6 限制结果集合记录条数(分页) |
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## 7.6 限制结果集合记录条数(分页) |
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- 方法:`SELECT * FROM table_name LIMIT [起始下标, ]搜寻条数` |
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- 方法:`SELECT * FROM table_name LIMIT [起始下标, ]搜寻条数` |
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注意: |
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- LIMIT一般放在最后 |
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```sql |
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```sql |
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# 查询前两条 |
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-- 查询前两条 |
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SELECT * FROM student_info LIMIT 2; |
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SELECT * FROM student_info LIMIT 2; |
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# 查询两条,从5+1开始 |
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-- 查询两条,从5+1开始 |
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SELECT * FROM student_info LIMIT 5, 2; |
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SELECT * FROM student_info LIMIT 5, 2; |
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``` |
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``` |
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## 7.7 对查询结果排序 |
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### 7.7.1 单列查询 |
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- 方法:`ORDER BY 列名 [ASC|DESC]` |
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ASC为默认升序,DESC为倒序 |
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```sql |
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SELECT student_info.number FROM student_info ORDER BY student_info.number ASC; |
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SELECT * FROM student_info ORDER BY student_info.number ASC; |
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SELECT * FROM student_info ORDER BY student_info.number DESC; |
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``` |
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### 7.7.2 多列查询 |
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- 方法:`ORDER BY 列1 [ASC|DESC], 列2 [ASC|DESC],...` |
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# 第八章 带搜索条件的查询 |
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## 8.1 简单搜索条件 |
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| 运算符 | 示例 | 描述 | |
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|-------|-------------|--------------| |
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|=| a = b | | |
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|<=>| a <=> b | 相等,NULL值安全相等 | |
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|<>或!=| a<>b 或 a!=b | 不等 | |
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|<| | 小于 | |
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|<=| | 小于等于 | |
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|>| | 大于 | |
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|>=| | 大于等于 | |
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|BETWEEN| a BETWEEN b AND C| a 属于[b, c]| |
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|NOT BETWEEN|a NOT BETWEEN b AND C| a 不属于[b, c]| |
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```sql |
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-- 查id等于20210101的学生的所有成绩 |
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SELECT * FROM student_score WHERE number = 20210101; |
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-- 查看除了这个学生的其他的学生的成绩 |
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SELECT * FROM student_score WHERE number != 20210101; |
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SELECT * FROM student_score WHERE number <> 20210101; |
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-- 查成绩及格 |
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SELECT * FROM student_score WHERE score >= 60; |
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-- 查成绩不及格 |
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SELECT * FROM student_score WHERE score < 60; |
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-- 查成绩在60到80之间的成绩 |
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SELECT * FROM student_score WHERE score BETWEEN 60 AND 80; |
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-- 查成绩不在60到80之间的成绩 |
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SELECT * FROM student_score WHERE score NOT BETWEEN 60 AND 80; |
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``` |
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## 8.2 匹配列表中的元素 IN |
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