Question

我有一个名为“客户”的表：

id | name    | age

1  | john    | 35        
2  | paul    | 22        
3  | ana     | 26   
4  | mark    | 19   
5  | jack    | 29

我想选择姓名和最大年龄，姓名和最小年龄...类似

john 35 mark 19

有可能吗？

Answer 1

以下查询将根据您的要求在一行中提供最大和最小。如果最小/最大有多个匹配项，您将获得多行。取决于所使用的SQL引擎，限制为一行的语法是不同的。

SELECT cMax.Name, cMax.Age, cMin.Name, cMin.Age
FROM customers cMin
JOIN customers cMax ON
    cMax.Age = (SELECT MAX(Age) FROM customers)
WHERE cMin.Age = (SELECT MIN(Age) FROM customers)

有不同类型的联接（例如INNER，OUTER，CROSS）；但是，对于您的问题，使用哪个都没关系。

Answer 2

尝试

    select name, age from customers where age=(select max(age) from customers) union
 select name, age from customers where age=(select min(age) from customers)

Answer 3

是的，你可以做到

select name, age from customers
where age in (select max(age) 
from customers union select min (age)from customers)

Answer 4

如果您希望它们位于同一行：

private PostCallback callback;
private Exception exception;

public setPostCallback(PostCallback callback){
    this.callback = callback;
}

@Override
protected JSONObject doInBackground(String... args){
     // keep everything as before but when an Exception occurs,
     // assign it to *exception* in the catch block
} 

@Override
public void onPostExecute(JSONObject jsonObject){
    // Note: this will be executed on the main thread
    if(exception == null){
        callback.onSuccess(jsonObject);
    } else {
        callback.onError(exception);
    }
}

select cmin.*, cmax.* from (select name, age as minage from customers order by age asc fetch first 1 row only ) cmin cross join (select name, age as maxage from customers order by age desc fetch first 1 row only ) cmax;是仅返回结果集第一行的标准语法。某些数据库具有定制语法，例如fetch first 1 row only或limit。

Answer 5

尝试使用此查询显示MAX年龄：- select * from customers where age=(select max(age) from customers);

要显示MIN年龄，请使用以下查询：- select * from customers where age=(select min(age) from customers);

Answer 6

您可以使用cross join，它将两个查询输出并排放置。建立Rodrigo的查询：

df %>%
  group_by(as.Date(Datetime)) %>%
  mutate(LightIntensity = Irradiance/max(Irradiance))

它可能不是性能最高的，但形状正确。当表的行不完全为1时，请小心交叉联接，因为它会创建要联接的表中各行的笛卡尔积。

选择最小值和最大值

6 个答案: