Question

您好我是数据库的新手。我需要通过查询使用case语句和数据库中的结果的最大值来显示数组。

下面是我使用的mysql db的表数据。

create table department (deptid int not null auto_increment,deptname varchar(20) not null,primary key ( deptid));

DEPARTMENT表数据：
```
deptid | deptname
-------+---------
1      | IT      
2      | HR      
3      | ADMIN   
```

客户表创建脚本。

create table customer (
    custid int not null auto_increment,
    custname varchar(20) not null,
    recordkey int,
    deptid int,
    primary key (custid),
    foreign key (deptid) references Department(deptid)
);

客户表数据：

custid | custname | recordkey | deptid 
-------+----------+-----------+-------
1      | A        | 1         | 1
2      | B        | 1         | 2
3      | C        | 1         | 1
-------+----------+-----------+--------

下面我尝试使用group by查询结果。

select c.recordkey,count(d.deptid),d.deptname from department d join
    customer c on d.deptid=c.deptid
    group by c.recordkey,d.deptid,d.deptname;

结果：

recordkey | count(d.deptid) | deptname 
----------+-----------------+---------           
1         | 2               | IT
1         | 1               | HR

我也尝试过案例陈述：

select c.recordkey,d.deptname,
    case when d.deptname='IT' then count(d.dept name)
    else 0 end as itcount,
    case when d.deptname='HR' then count(d.deptname)
    else 0 end as hrcount from department d
    join customer c on d.deptid=c.deptid
    group by c.recordkey,d.deptname;

结果：

recordkey | deptname | itcount | hrcount
----------+----------+---------+--------
1         | HR       | 0       | 1
1         | IT       | 2       | 0

根据要求，结果必须是单行。

但最终结果应为deptid，其中count和max来自计数。例如，IT部门有最大记录。

recordkey | itdeptid | itdeptname | itocunt | hrdeptid | hrdeptname | hrcount | admindeptid | admindeptname | admincount | max of (itocunt hrcount admincount)
----------+----------+------------+---------+----------+------------+---------+-------------+---------------+------------+------------------------------------
1         | 1        | IT         | 2       | 2        | HR         | 1       | 3           | ADMIN         | 0          | 2

如果有人有任何建议，那就太好了。

按行查询分组，SQL中包含最大计数

0 个答案: