SQL WHERE Help: how do i pull data from multiple rows in one single query?

问题

I am not sure if this is supposed to use a subquery, or multiple temp tables...but any assistance would be great! i am trying to do the following in one query pull.

I want to pull, say, all rows where a User has Color=blue and Color=red. I am interested in pulling these multiple rows to determine which users CHANGED their Color from blue to red, or from red to blue.

The general query i have now is this. What is wrong and how can i improve it? thank you!

1. Does this return Zero results because I am asking that the row's value has BOTH blue and red at the same time? (which is impossible)
2. my other worry, is that if I use OR instead of AND, that i will include rows for users that are color blue, or color red, but did NOT change between the two colors.

SELECT *
FROM Table a
WHERE a.color='blue'
AND a.color='red'

回答1:

I'm assuming userId as the id which defines user, you can replace with whatever you have in the table. The problem is called Relational Division. Hope this helps!

    select * from table where color in ('blue','red') and userId in(select a.userId 
    from Table a
    where a.color in ('blue','red')
    group by a.userid  //whatever defines user uniquely
    having count(distinct a.color)=2)

回答2:

MySQL does not store history like what you are wanting it to do. What you need to do is to have another table for color history and log entries every time the user changes colors. I would post code with table structure but there are so many different ways that this could be done... So a question without table structure does not get an answer with table structure proposal.

来源：https://stackoverflow.com/questions/20154571/sql-where-help-how-do-i-pull-data-from-multiple-rows-in-one-single-query