27 lines
584 B
Markdown
27 lines
584 B
Markdown
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# 一、连接查询的类型
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1. 交叉连接
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2. **内连接**（MySQL中常用）
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3. 左外连接
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4. 右外连接
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5. 全外连接
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# 二、内连接
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1. SQL标准中规定的语法（**重点**）：
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```sql
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select 字段名
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from 表1,[inner] join 表2 on 连接条件表达式[······]
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[where 条件表达式];
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```
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2. 传统用法：
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```sql
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select 字段名
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from 表1, 表2[, ······]
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where 连接条件表达式;
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```
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# 三、左外连接
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语法：
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```sql
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select 字段名
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from 表1, left [outer] join 表2 on 连接条件表达式[······]
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[where 条件表达式];
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```
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