将数组中的随机值设置为数据库

Question

我正在使用MYSQL数据库处理PHP项目。我有一组学生表。每个小组都有一名考官。我想要做的是我想为每个组随机设置两名考官。怎么做？

MySQL代码：

create table groups (
    groupID    int(10)    not null, 
    nbStudents   int     not null, 
    avgGPA    DOUBLE    NOT NULL, 
    projectName   varchar(50)   not null, 
    advisorID   int,     
    examiner1ID   int,  
    examiner2ID   int, 
    adminID    int     not null, 
    primary key (groupID) 
); 

create table faculty (
    name    varchar(30)   not null, 
    facultyID   int(10)     not null, 
    email    varchar(30)   not null, 
    mobile    int(15)    not null,    
    primary key (facultyID) 
); 

examiner1ID和examiner2ID是从表中的教师外键。

Answer 1

这是一个非常复杂的方式来做到这一点。它使用2个子查询来挑选教师成员，并使用insert .. on duplicate key来更新考官ID。

insert into groups 
(groupID, examiner1ID, examiner2ID) 
select groupID, 
    @x:=(select facultyID from faculty order by rand() limit 1), 
    (select facultyID from faculty where facultyID <> @x order by rand() limit 1) 
from groups 
on duplicate key update examiner1ID=values(examiner1ID), examiner2ID=values(examiner2ID); 

@x是user-defined-variable。在这种情况下，它被用来存储第一个随机的教员。 <> @x确保我们不会在两个插槽中选择相同的教员。

由于groupID是一个唯一的键，当我们尝试插入一个具有现有唯一键的行时，它将更新现有的行而不是插入它。这就是on duplicate key update子句的用法。对于每个组

设置不同的审查员：

insert into groups 
(groupID, examier1ID, examier2ID) 
select a.groupID, max(if(b.id%2, b.facultyID, 0)), max(if(b.id%2, 0, b.facultyID)) 
from (
    select @row:=@row+1 id, groupID 
    from groups a 
    join (select @row:=0) b) a 
join (
    select @row:=@row+1 id, facultyID 
    from (
     select facultyID 
     from faculty a 
     order by rand()) a 
    join (select @row:=0) b) b on a.id = ceil(b.id/2) 
group by a.groupID 
on duplicate key update examiner1ID=values(examiner1ID), examiner2ID=values(examiner2ID);