loop.md

# 循环

下面哪一项定义的函数可以生成指定范围内的整数数列？

## 答案

```postgresql
create function gen(start integer, stop integer)
    returns setof integer as
$$
begin
    for idx in start .. stop
        loop
            return next idx;
        end loop;
end;
$$ language plpgsql;
```

## 选项

### A

```postgresql
create function gen(start integer, stop integer) returns integer as
$$
begin
    for idx in start .. stop
        loop
            return idx;
        end loop;
end;
$$ language plpgsql;
```

### B

```postgresql
create function gen(start integer, stop integer)
    returns integer as
$$
begin
    for idx in start .. stop
        loop
            yield idx;
        end loop;
end;
$$ language plpgsql;
```

### C

```postgresql
create function gen(start integer, stop integer)
    returns setof integer as
$$
begin
    for idx in start .. stop
        loop
            return idx;
            idx += 1;
        end loop;
end;
$$ language plpgsql;
```

### D

```postgresql
create function gen(start integer, stop integer)
    returns setof integer as
$$
begin
    for idx in start .. stop
        loop
            select idx;
        end loop;
end;
$$ language plpgsql;
```