avg.md

# 平均值练习

Joe 想要得到 employee 表

```sql
create table employee
(
    id     serial primary key,
    name   varchar(256),
    dept   varchar(256),
    salary decimal(12, 4)
);
```

中每个部门的平均工资信息，这条查询应该怎么写？

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* `show databases;` 列出所有数据库
* `show tables;` 列出所有表

## 答案

```sql
select dept, avg(salary) 
from employee 
group by dept;
```

## 选项

### A

```sql
select dept, avg(salary) 
from employee;
```

### B

```sql
select dept, avg(dept) 
from employee 
group by dept;
```

### C

```sql
select dept, avg(salary) 
from employee 
group by salary;
```