我创建了两张桌子和一张桌子.插入的值如下所示.

表格1

create table maxID (myID varchar(4));

insert into maxID values ('A001');
insert into maxID values ('A002');
insert into maxID values ('A004');
insert into maxID values ('A003');

表2

create table maxID2 (myID varchar(4) PRIMARY KEY);

insert into maxID2 values ('A001');
insert into maxID2 values ('A002');
insert into maxID2 values ('A004');
insert into maxID2 values ('A003');

当我执行查询

SELECT myId,@rowid:=@rowid+1 as myrow 
FROM maxID,(SELECT @rowid:=0) as init
ORDER BY myrow desc
LIMIT 1;

我输出为

+++++++++++++
myid + myrow
+++++++++++++
A003 + 4
+++++++++++++

和

当我执行查询

SELECT myId,@rowid:=@rowid+1 as myrow 
FROM maxID2,(SELECT @rowid:=0) as init
ORDER BY myrow desc
LIMIT 1;

我输出为

+++++++++++++
myid + myrow
+++++++++++++
A004 + 4
+++++++++++++

两个表之间的区别在于,在第二个表中,我将myID作为PRIMARY KEY.

您可以在www.sqlfiddle.com查看上述数据/结果.

我的问题是

为什么在查询相同时我得到两个不同的结果？

注意：这个问题与我的旧问题Getting last record from mysql有点相关,我几乎得到了答案,Yak通知我,行的顺序无法保证.