关于数据库ioin操作下面说法错误的是 ( 存在inner join和outer ioin 存在left join和right join inner join的效果是两个表的交集 left outer join和right outer join的效果是两个表的并集
时间: 2023-11-15 21:58:12 浏览: 84
关于数据库join操作,下面说法错误的是“inner join的效果是两个表的交集,left outer join和right outer join的效果是两个表的并集”。实际上,inner join的效果是返回两个表中联结字段相等的行,left outer join和right outer join的效果是返回包括左表或右表中的所有记录和另一个表中联结字段相等的记录。因此,left outer join和right outer join的效果是两个表的联合,而不是并集。
相关问题
inner join,left outer join,right outer join,full outer join
inner join是一种等值连接,它只返回两个表中联结字段相等的行。left outer join是左外连接,它返回包括左表中的所有记录和右表中联结字段相等的记录。right outer join是右外连接,它返回包括右表中的所有记录和左表中联结字段相等的记录。full outer join是全外连接,它返回包括左表和右表中的所有记录,无论是否有匹配的记录。所以,这些连接类型主要区别在于它们返回的记录集合的不同。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
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inner join、 left join 、right join、 outer join语法
以下是SQL中inner join、left join、right join、outer join的语法:
1. inner join语法:
```sql
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;
```
2. left join语法:
```sql
SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;
```
3. right join语法:
```sql
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;
```
4. outer join语法:
```sql
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name = table2.column_name;
```
其中,inner join返回两个表中联结字段相等的行,left join返回包括左表中的所有记录和右表中联结字段相等的记录,right join返回包括右表中的所有记录和左表中联结字段相等的记录,outer join返回两个表中联结字段相等的行以及未联结的行。
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