MYSQL

Question

数据方案：

create table level (
  id int auto_increment primary key,
  # ... other data which is not relevant
);

create table session (
  id int auto_increment primary key,
  lvlid1 int not null,
  lvlid2 int not null,
  lvlid3 int not null,
  lvlid4 int not null,
  ts timestamp not null default current_timestamp,
  foreign key(lvlid1) references level(id),
  foreign key(lvlid2) references level(id),
  foreign key(lvlid3) references level(id),
  foreign key(lvlid4) references level(id)
);

我如何 select 4 个随机不同的 id 从级别 table 进入会话 table 的（lvlid1、lvlid2、lvlid3、lvlid4）？更具体地说，我想知道是否可以这样做：

insert into session (lvlid1, lvlid2, lvlid3, lvlid4)
values(TRANSPOSE(select id from level order by rand() limit 4))

Answer 1

您可以使用具有动态行号变量的数据透视查询来 select 单独列中的四个随机 ID。

SET @row_number = 0;

INSERT INTO session (lvlid1, lvlid2, lvlid3, lvlid4)
SELECT MAX(CASE WHEN t2.rn = 1 THEN t2.id END),
       MAX(CASE WHEN t2.rn = 2 THEN t2.id END),
       MAX(CASE WHEN t2.rn = 3 THEN t2.id END),
       MAX(CASE WHEN t2.rn = 4 THEN t2.id END)
FROM
(
    SELECT t.id, (@row_number:=@row_number + 1) AS rn
    FROM
    (
        SELECT id FROM lv_kb00_level ORDER BY RAND()
    ) AS t
) AS t2

MYSQL - Select 4 个随机行并将它们转置到插入语句的列中

MYSQL - Select 4 random rows and transpose them into columns of insert statement

database

select

transpose

sql-insert