geo.md

# 数值计算

Points 表结构如下：

```sql
create table points(
    id int primary key auto_increment,
    x float,
    y float
)
```

现在 Joe 想要求写一个查询，得到每个点的id和模。即 √(x^2+y^2) 。这个查询应该是：

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

## 答案

```sql
select id, sqrt(x^2 + y^2) 
from points;
```

## 选项

### A

```sql
select sqrt(vx+vy) 
from (
    select x^2 as vx, y^2 as vy 
    from points) as t;
```

### B

```sql
select sqrt(vx + vy) 
from points 
where x^2 as vx, y^2 as vy ;
```

### C

```sql
select id + sqrt(x^2 + y^2) 
from points;
```

### D

```sql
select id || sqrt(x^2 + y^2) 
from points;
```