Select 字段，其中列具有多个元素 SQL

Question

look this:

Given the table "Customer" that has the following columns:

• Name1  First name of the customer.
• Name2  Second Name of the customer.
• Surname1  Customer's First Surname.
• Surname2  Second Surname of the client.
• T_Documento  Type of customer document
• N_Document  Customer document number
• Country_Residence  Country where the Client Resides

PROBLEN TO SOLVE: Write a check that lists the Countries of Residence with less than 10 clients.

I have been looking for the right code but I still with out find any solution

SELECT * (
SELECT pais_residencia, COUNT(*) AS ClientesTotales
FROM Clientes
GROUP BY pais_residencia
) FROM Clientes
WHERE ClientesTotales > 10

this is wrong btw...

any idea

Answer 1

Your code should work, provided that you change > to < in the outer query (and add FROM in the outer query to introduce the subquery).

But it can be simplified. You don't need a subquery to filter on the count, you can use a having clause instead:

SELECT pais_residencia, COUNT(*) AS ClientesTotales
FROM Clientes
GROUP BY pais_residencia 
HAVING COUNT(*) < 10

MySQL even supports reusing alias in the HAVING clause, which can be phrased:

HAVING ClientesTotales < 10

Answer 2

If you want less than 10 clientes then you want:

SELECT * 
FROM (SELECT pais_residencia, COUNT(*) AS ClientesTotales
      FROM Clientes
      GROUP BY pais_residencia
     ) r
WHERE ClientesTotales < 10;

The direction of your comparison is wrong, based on the question.

In addition, there are some other syntactic problems with your query -- the subquery should be part of the FROM clause, for instance.

You don't need a subquery for this. You can just use HAVING :

If you want less than 10 clientes then you want:

SELECT pais_residencia, COUNT(*) AS ClientesTotales
FROM Clientes
GROUP BY pais_residencia
HAVING ClientesTotales < 10;

Answer 3

If you need to display all data from a table, you can use this code

select
     name1,
     name2,
     surname1,
     surname2,
     t_documento,
     N_Document,
     country_residence
 FROM
     (
         SELECT
             name1,
             name2,
             surname1,
             surname2,
             t_documento,
             n_document,
             country_residence,
             COUNT(country_residence) OVER(
                 PARTITION BY country_residence
             ) clientestotales
         FROM
             clientes
     )
 WHERE
     clientestotales < 10;