1. 新增(create)
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insert into [表名] (字段1, 字段2,....) value (value1, value2, ...);insert into [表名] (字段1, 字段2, ....) values(value1, ...),(value2, ...),(value3, ...); |
实例:
创建一个学生成绩表
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create table exam_result ( id int, name varchar(20), chinese decimal(3,1), math decimal(3,1), english decimal(3,1)); |
1.1 单行数据 + 全列插入
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-- 插入两条记录，value_list 数量必须和定义表的列的数量及顺序一致insert into exam_result value ( 1, 'tom', 68, 98, 56); insert into exam_result value ( 2, 'jum', 87.5, 78, 77); |
每次插入数据, 为一条记录, 包含了若干个列~~
列的数目和数据类型要和表的结构对应~
value 前省略指定列默认为全列插入
1.2 多行数据 + 指定列
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- 插入两条记录，value_list 数量必须和指定列数量及顺序一致insert into exam_result (id,name, chinese, math, english) values (1,'tom', 67, 98, 56), (2,'jum', 87.5, 78, 77), (3,'lim', 88, 98.5, 90), (4,'tim', 82, 84, 67), (5,'huy', 55.5, 85, 45), (6,'sun', 70, 73, 78.5), (7,'ming', 75, 65, 30); |
2. 查询(retrieve)
2.1 全列查询
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select * from [表名]; |
*表示通配符, 意思就是查找所有的列
2.2 指定列查询
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select [指定查询列] from [表名]; |
2.3 查询字段为表达式
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select [字段表达式] from [表名]; |
2.4 别名
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select colum [as] [列名] from [表名]; |
2.5 去重: distinct
使用 distinct 关键字对某列数据去重
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--98 分重复了select math from exam_result;+------+| math |+------+| 98.0 || 78.0 || 98.0 || 84.0 || 85.0 || 73.0 || 65.0 |+------+-- 去重结果select distinct math from exam_result;+------+| math |+------+| 98.0 || 78.0 || 84.0 || 85.0 || 73.0 || 65.0 |+------+ |
2.6 排序: order by
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select * from [表名] order by [排序字段]; |
用 order by 指定某一列进行排序, 默认按照升序排序.
显式加上 desc , 就是降序排序. 使用 asc 也是升序
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select name, math from exam_result order by math desc;+------+------+| name | math |+------+------+| tom | 98.0 || lim | 98.0 || huy | 85.0 || tim | 84.0 || jum | 78.0 || sun | 73.0 || ming | 65.0 |+------+------+ |
null 数据排序，视为比任何值都小，升序出现在最上面，降序出现在最下面
排序也可以指定多个列执行
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select * from exam_result order by math desc, chinese desc;+------+------+---------+------+---------+| id | name | chinese | math | english |+------+------+---------+------+---------+| 3 | lim | 88.0 | 98.0 | 90.0 || 1 | tom | 67.0 | 98.0 | 56.0 || 5 | huy | 55.5 | 85.0 | 45.0 || 4 | tim | 82.0 | 84.0 | 67.0 || 2 | jum | 87.5 | 78.0 | 77.0 || 6 | sun | 70.0 | 73.0 | 78.5 || 7 | ming | 75.0 | 65.0 | 30.0 |+------+------+---------+------+---------+ |
多列排序时, 是在第一列区分不出来大小的时候, 再按第二列排序.
2.7 条件查询: where
比较运算符
| 运算符 | 说明 |
|---|---|
| >, >=, <, <= | 大于，大于等于，小于，小于等于 |
| = | 等于，null 不安全，例如 null = null 的结果是 null |
| <=> | 等于，null 安全，例如 null <=> null 的结果是 true(1) |
| !=, <> | 不等于 |
| between a0 and a1 | 范围匹配，[a0, a1]，如果 a0 <= value <= a1，返回 true(1) |
| in (option, …) | 如果是 option 中的任意一个，返回 true(1) |
| is null | 是 null |
| is not null | 不是 null |
| like | 模糊匹配。% 表示任意多个（包括 0 个）任意字符；_ 表示任意一个字符 |
逻辑运算符:
| 运算符 | 说明 |
|---|---|
| and | 多个条件必须都为 true(1)，结果才是 true(1) |
| or | 任意一个条件为 true(1), 结果为 true(1) |
| not | 条件为 true(1)，结果为 false(0) |
注意:
- 列的别名不能再 where 中使用~~
- and的优先级高于or，在同时使用时，需要使用小括号()包裹优先执行的部分
实例:
基本查询：
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-- 查询英语不及格的同学及英语成绩 ( < 60 )select name, english from exam_result where english < 60;-- 查询语文成绩好于英语成绩的同学select name, chinese, english from exam_result where chinese > english;-- 查询总分在 200 分以下的同学select name, chinese + math + english as total from exam_result where chinese + math + english < 200; |
and 与 or：
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-- 查询语文成绩大于80分，且英语成绩大于80分的同学select * from exam_result where chinese > 80 and english > 80;-- 查询语文成绩大于80分，或英语成绩大于80分的同学select * from exam_result where chinese > 80 or english > 80; |
关于优先级问题, and 比 or 更优先,
范围查询:
1.between … and …
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-- 查询语文成绩在 [80, 90] 分的同学及语文成绩select name, chinese from exam_result where chinese between 80 and 90;select name, chinese, from exam_result where chinese >= 80 and chinese <= 90; |
in
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-- 查询数学成绩是 58 或者 59 或者 98 或者 99 分的同学及数学成绩select name, math from exam_result where math in (58, 59, 98, 99); |
模糊查询: like
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select name from exam_result where name like 't%';+------+| name |+------+| tom || tim |+------+ |
% 是一个通配符, 可以用来代替任意多个字符
t% 找出以 t 开头的字符串
%t 找出以 t 结尾的字符串
%t% 找出包含 t 的
除了 % 之外, 还有 _ ，（_ 只能代表一个字符~)
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select name from exam_result where name like 't__';+------+| name |+------+| tom || tim |+------+ |
通配符也能针对数字进行模糊查询
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select name, chinese from exam_result where chinese like '%8%';+------+---------+| name | chinese |+------+---------+| jum | 87.5 || lim | 88.0 || tim | 82.0 |+------+---------+ |
注意:
模糊查询看起来比较好用, 实际执行效率低下
null 的查询: is [not] null
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select name from exam_result where id id not null; |
2.8 分页查询: limit
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-- 最初数据表select * from exam_result;+------+------+---------+------+---------+| id | name | chinese | math | english |+------+------+---------+------+---------+| 1 | tom | 67.0 | 98.0 | 56.0 || 2 | jum | 87.5 | 78.0 | 77.0 || 3 | lim | 88.0 | 98.0 | 90.0 || 4 | tim | 82.0 | 84.0 | 67.0 || 5 | huy | 55.5 | 85.0 | 45.0 || 6 | sun | 70.0 | 73.0 | 78.5 || 7 | ming | 75.0 | 65.0 | 30.0 |+------+------+---------+------+---------+-- 前三条记录select * from exam_result limit 3;+------+------+---------+------+---------+| id | name | chinese | math | english |+------+------+---------+------+---------+| 1 | tom | 67.0 | 98.0 | 56.0 || 2 | jum | 87.5 | 78.0 | 77.0 || 3 | lim | 88.0 | 98.0 | 90.0 |+------+------+---------+------+---------+-- 从第三条开始的三条记录select * from exam_result limit 3 offset 3;+------+------+---------+------+---------+| id | name | chinese | math | english |+------+------+---------+------+---------+| 4 | tim | 82.0 | 84.0 | 67.0 || 5 | huy | 55.5 | 85.0 | 45.0 || 6 | sun | 70.0 | 73.0 | 78.5 |+------+------+---------+------+---------+ |
offset 表示从第几条开始查找, offset 可以省略
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select * from exam_result limit 3 , 4;+------+------+---------+------+---------+| id | name | chinese | math | english |+------+------+---------+------+---------+| 4 | tim | 82.0 | 84.0 | 67.0 || 5 | huy | 55.5 | 85.0 | 45.0 || 6 | sun | 70.0 | 73.0 | 78.5 || 7 | ming | 75.0 | 65.0 | 30.0 |+------+------+---------+------+---------+ |
3. 修改(update)
– 将总成绩倒数前三的 3 位同学的数学成绩加上 30 分
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update exam_result set math = math + 30 order by chinese + math + english limit 3; |
update 不加条件, 就可以针对所有
4. 删除(delete)
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delete from [表名]; |
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-- 删除 ming 同学的考试成绩delete from exam_result where name = 'ming';-- 删除整张表delete from exam_result; |
如果不指定条件, 此时就把整个表删除掉了, (与 drop 删除表还有不同)
delete 删除后表为 null, drop 删除后表就不存在了
5. 常用 新增
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-- 单行插入insert into [表名] (字段1, ..., 字段n) values (value1, ...,value n);-- 多行插入insert into [表名](字段1, ..., 字段n) values(value1, ...),(value2, ...),(value3, ...); |
查询
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--全表查询select * from [表名];--指定列查询select [列名1, 列名2,...] from [表名];--查询表达式字段select [表达式1, 表达式2,...] from [表名];--别名select--去重 distinctselect distinct [字段] from [表名];-- 排序order byselect * from [表名] order by [排序字段];-- 条件查询where-- (1)比较运算符 (2)between ... and ... (3)in (4)is null (5)like (6)and (7)or (8)notselect * from [表名] where [条件]; |
修改
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update [表] set [修改内容1, 修改内容2, ....] where [条件]; |
删除
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delete from [表名] where [条件]; |
总结
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原文链接：https://blog.csdn.net/weixin_47230102/article/details/115416031
