在 select 后面使用数字是什么意思？

Question

有两个表：

create table author (id int primary key auto_increment, name varchar(255));
insert into author (name) values ('tingwei');
insert into author (name) values ('jiahui');
insert into author (name) values ('naidan');
insert into author (name) values ('weizhi');
insert into author (name) values ('siyao');

create table book (author_id int primary key auto_increment, book varchar(255));
insert into book (book) values ('I love you');
insert into book (book) values ('I hate you');
insert into book (book) values ('I miss you');

但是不知道这个语句后面用数字1是什么意思"select":

select *
from author
where exists (select 1 from book where book.author_id = author.id)

我已经在网上搜索了一些资料，但一无所获。

Answer 1

SELECT 1 就是这样做的：它选择值 1。当与 WHERE EXISTS 一起使用时，子查询 returns 的数据无关紧要，只要它 returns 任何数据（换句话说：returns 至少一行）。 =13=]

在 select 后面使用数字是什么意思？

What does it mean using number behind select?

mysql

select

exists