Question

我开始阅读更深入的MySql并尝试在description上解决此任务。根据描述需要从表中删除重复项，但我的查询不起作用。在sqllite工作正常。是什么原因？

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Entity;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.Form;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.glassfish.jersey.client.authentication.HttpAuthenticationFeature;

public static void sendSimpleMessage(String recipient) {
        Client clientMail = ClientBuilder.newBuilder().build();
              clientMail.register(HttpAuthenticationFeature.basic("api", MAILGUN_API_KEY));

        WebTarget targetMail = clientMail.target("https://api.mailgun.net/v3/" + MAILGUN_DOMAIN_NAME + "/messages");

        Form formData = new Form();
              formData.param("from", "Mailgun Sandbox <"+DOMAIN_MAIL_ADDRESS+">");
              formData.param("to", recipient);
              formData.param("subject", "Simple Mailgun Example");
              formData.param("text", "Plaintext content");

        Response response = targetMail.request().post(Entity.entity(formData, MediaType.APPLICATION_FORM_URLENCODED_TYPE));
        System.out.println("Mail sent : " + response);

    }

错误

DELETE
FROM
    Person
WHERE
    Email IN(
    SELECT
        Email
    FROM
        Person
    GROUP BY
        Email
    HAVING
        COUNT(Email) > 1
);

Answer 1

您可以使用自联接来删除重复项

delete a
from Person a
left join Person b on a.Email = b.Email
                 and a.id > b.id
where b.Email is not null

Demo

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

您不能在FROM子句中为更新指定目标表'table_name'

1 个答案: