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134 lines
2.8 KiB
Markdown
134 lines
2.8 KiB
Markdown
---
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title: SQL 基础笔记
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created: 2022-07-13
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summary: 关于增改删查的方式
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tags:
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- SQL
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---
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- 课程：[The Complete 2022 Web Development Bootcamp](https://www.udemy.com/share/1013gG3@wP9ybulEki65OWpaP1-gXEeRPJl4aj8eZNX7YYjFOgXlrxBGQyU6NniyJf2PqDI1EA==/)
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- 工具：[SQL Online Compiler - for Data Science](https://sqliteonline.com)
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- 教程：[SQL 教程 | 菜鸟教程](https://www.runoob.com/sql/sql-tutorial.html)
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## SQL vs. NOSQL
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- SQL
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- 注重结构
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- NOSQL
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- 更灵活，也更稳健
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- MoogoDB
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## CRUD
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### Create
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```sql
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CREATE TABLE product(
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id Int NOT NULL,
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name STRING,
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price MONEY,
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PRIMARY KEY(id)
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)
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```
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- `NOT NULL` 当此值为 null 时，不创建列
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- `PRIMARY KEY(id)` 主键必须包含唯一的值，这个不能有重复的值
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**插入数值**
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第一种形式无需指定要插入数据的列名，只需提供被插入的值即可
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```sql
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INSERT INTO _table_name_
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VALUES (_value1_,_value2_,_value3_,...);
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```
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第二种形式需要指定列名及被插入的值：
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```sql
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INSERT INTO _table_name_ (_column1_,_column2_,_column3_,...)
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VALUES (_value1_,_value2_,_value3_,...);
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```
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### Read
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SELECT 语句用于从数据库中选取数据。
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```sql
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SELECT _column_name_,_column_name_
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FROM _table_name_;
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```
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```sql
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SELECT * FROM _table_name_;
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```
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`*` 表示选择全部
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可以用`WHERE` 筛选选择结果，如：
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```sql
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SELECT _column_name_,_column_name_
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FROM _table_name_
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WHERE _column_name operator value_;
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```
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### Update
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```sql
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UPDATE _tablse_name_
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SET _column1_=_value1_,_column2_=_value2_,...
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WHERE _some_column_=_some_value_;
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```
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**ALTER TABLE 语句用于在已有的表中添加、删除或修改列。**
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如需在表中添加列，请使用下面的语法:
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```sql
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ALTER TABLE table_name
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ADD column_name datatype
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```
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如需删除表中的列，请使用下面的语法（请注意，某些数据库系统不允许这种在数据库表中删除列的方式）：
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```sql
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ALTER TABLE table_name
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DROP COLUMN column_name
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```
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### Destory
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```sql
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DELETE FROM _table_name_
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WHERE _some_column_=_some_value_;
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```
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## Understanding SQL Relationships, Foreign Keys and Inner Joins
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### FOREIGN KEY
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- 用`FOREIGN KEY` 来和外部表单链接
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- 一个表中的 FOREIGN KEY 指向另一个表中的 UNIQUE KEY(唯一约束的键)。
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### INNER JOIN
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选择相应列并合并表，`ON`后面写的是条件
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```sql
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SELECT _column_name(s)_
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FROM _table1_
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INNER JOIN _table2_
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ON _table1.column_name_=_table2.column_name_;
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```
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或：
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```sql
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SELECT _column_name(s)_
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FROM _table1_
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JOIN _table2_
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ON _table1.column_name_=_table2.column_name_;
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```
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