mysql IN运算符按降序返回值

Question

I am trying to run a query off of my mysql database using the IN operator.

SELECT usernum FROM usergroup WHERE emailmain IN ('blah@blah.com', 'rawr@rawr.com', 'e@e.com')

The query works but instead of outputing the usernum values in the order entered it outputs them in descending order. This is problematic because I need them to be aligned to the emails. I think it may have to do with the limit operator or by using an ORDER BY emailmain . I've tried that and it still doesn't work because assuming the email doesn't exist in the database it won't correspond to the memory location in the array.

The most important thing to me is that I know the emails that aren't in the database.

Any help would be appreciated!

Answer 1

You can use ORDER BY FIELD to define your order

SELECT usernum 
FROM usergroup 
WHERE emailmain IN ('blah@blah.com', 'rawr@rawr.com', 'e@e.com')
ORDER BY FIELD (emailmain, 'blah@blah.com', 'rawr@rawr.com', 'e@e.com')

Answer 2

IN won't impact the order of your results at all, without an ORDER clause rows will come back in whatever order they're found in.

If you need to match the order of the results to the order of your supplied email list, try this:

SELECT usernum
  FROM usergroup
  WHERE emailmain IN ('blah@blah.com', 'rawr@rawr.com', 'e@e.com')
  ORDER BY FIND_IN_SET(emailmain, "blah@blah.com,rawr@rawr.com,e@e.com")

FIND_IN_SET will return the position of the given string in a comma-delimited list

With larger lists it would probably be safer though to just use SELECT usernum, emailmain FROM ... to return both fields in each result and correlate them application-side.

Answer 3

If you are creating the IN string dynamically, you don't have to create a table every time you run the query - you can use an inline view, populated in the same way as the IN string, like so:

select v.email, u.usernum
from 
(select 'blah@blah.com' email union select 'rawr@rawr.com' union select 'e@e.com') v
left join usergroup u on v.email = u.emailmain
order by v.email

Answer 4

为什么不从数据库中选择用户名和电子邮件？

SELECT usernum, emailmain FROM usergroup WHERE emailmain IN ('blah@blah.com', 'rawr@rawr.com', 'e@e.com') ORDER BY emailmain DESC

Answer 5

Providing IN condition does not imply the order.

To order your result, use ORDER BY at the end of your query.