我想编写一个 SQL 查询来确定员工人数最多的公司，然后显示它是以前公司的员工

Question

我有一个包含以下两个表的架构

1.人 -

+-------+----------------+------------+-----------------+-----------------+
| ID    | NAME           | DOJ        | PREV_COMPANY_ID | CURR_COMPANY_ID |
+-------+----------------+------------+-----------------+-----------------+
| 1795f | ALEX BROWN     | 1973-03-02 | 4e5b            | 123a            |
| 8772  | Chris Mitchell | 2016-06-15 | 4746            | 4e5b            |
| 5e03  | Patt Hobbs     | 1976-09-14 | 4e5b            | 123b            |
+-------+----------------+------------+-----------------+-----------------+

2。公司 -

+-------+---------------+
| ID    | NAME          |
+-------+---------------+
| 4746  | Mora-Sullivan |
| 49de6 | Harmon-Miller |
| 4e5b  | Fakesmith     |
+-------+---------------+

我想编写查询以找到以下内容-

1. 首先确定员工人数最多的公司，然后显示其在前公司的员工。

我找到了使用 sql 查询的员工人数最多的公司。即这里的Fakesmith。

SELECT PREV_COMPANY_ID, COUNT(*) as count 
FROM PEOPLE 
GROUP BY PREV_COMPANY_ID
ORDER BY count DESC;

但我无法建立任何逻辑来找到使用以前公司名称的员工人数最多的当前雇主。我该如何解决这个问题？

Answer 1

您是否正在尝试这样的事情：

create table people(
id varchar(9) not null ,
name varchar(50) not null ,
doj date ,
PREV_COMPANY_ID varchar(50),
CURR_COMPANY_ID varchar(50),
Primary key id(`id`)
);

insert into people values ('1795f','ALEX BROWN','1973-03-02','4e5b','123a'),('8772','Chris Mitchell','2016-06-15','4746','4e5b'),('5e03','Patt Hobbs','1976-09-14','4e5b','123b');


create table company(
id varchar(9) not null ,
name varchar(50) not null ,
Primary key id(`id`)
);

insert into company values ('4746','Mora-Sullivan'),('49de6','Harmon-Miller'),('4e5b','Fakesmith');


select p.name,p.CURR_COMPANY_ID,company.name as company_name 
from people p join (select PREV_COMPANY_ID ,count(*) as comp_high_nr from people group by PREV_COMPANY_ID  order by comp_high_nr desc limit 1) as t on p.CURR_COMPANY_ID =t.PREV_COMPANY_ID join company on p.PREV_COMPANY_ID=company.id  ;

Answer 2

试试这个对你有帮助

CREATE TABLE tblcompany (
  id varchar(9) NOT NULL,
  name varchar(50) NOT NULL,
  PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

INSERT INTO tblcompany (id,name) VALUES 
 ('1','Mora-Sullivan'),
 ('2','Harmon-Miller'),
 ('3','Fakesmith');

CREATE TABLE tblpeople (
  id varchar(9) NOT NULL,
  name varchar(50) NOT NULL,
  doj date DEFAULT NULL,
  PREV_COMPANY_ID varchar(50) DEFAULT NULL,
  CURR_COMPANY_ID varchar(50) DEFAULT NULL,
  PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

INSERT INTO tblpeople (id,name,doj,PREV_COMPANY_ID,CURR_COMPANY_ID) VALUES 
 ('1','ALEX BROWN','1973-03-02','1','2'),
 ('2','Chris Mitchell','2016-06-15','1','3'),
 ('3','Patt Hobbs','1976-09-14','2','3');

首先，我们需要找到员工最高的公司

SELECT t1.CURR_COMPANY_ID, COUNT(t1.id) as `NoOfEmployee` FROM tblpeople as t1 GROUP BY t1.CURR_COMPANY_ID ORDER BY NoOfEmployee DESC LIMIT 1;

然后我们加入人员表以获取该公司的所有员工

SELECT t1.*, t2.name as `CURR_COMPANY`, t3.name as `PREV_COMPANY` FROM tblpeople as t1 LEFT JOIN tblcompany as t2 ON t1.CURR_COMPANY_ID=t2.id LEFT JOIN tblcompany as t3 ON t1.PREV_COMPANY_ID=t3.id INNER JOIN (SELECT CURR_COMPANY_ID, COUNT(id) as EmployeeCount FROM tblpeople GROUP BY CURR_COMPANY_ID ORDER BY EmployeeCount DESC LIMIT 1) as t4 ON t1.CURR_COMPANY_ID=t4.CURR_COMPANY_ID;

Answer 3

请检查以下查询是否符合您的目的

SELECT *
  FROM PEOPLE
 WHERE CURR_COMPANY_ID IN (  SELECT PREV_COMPANY_ID
                               FROM (  SELECT PREV_COMPANY_ID, COUNT (1) AS C
                                         FROM PEOPLE
                                     GROUP BY CURR_COMPANY_ID
                                     ORDER BY C DESC)
                           ORDER BY c DESC)