MySQL：如何获得最后一条记录？

Question

Say I have the following records:

1, A
1, B
2, A
2, B
2, C
1, C

I want the last record for 1 and 2 , which should be 1, C and 2, C . How do I query that?

If I do a GROUP BY on the number, I get 1, A and 2, A .

Answer 1

if by 'last' you mean maximum alphabetically, then maybe this:

select id, max(val)
from mytable
group by id

Answer 2

Without some sort of index or insertion order, there's no way of getting what you want; SQL queries are order non-deterministic.

Answer 3

Now that we've established that you mean "last" as in "chronologically", then I can create a proper answer...

SQL has no concept of chronology. So you will have to record the insertion order yourself. Most typically, you would add an autoincrementing field, and then use that in an ORDER BY clause, along with a LIMIT clause.

Answer 4

If it's not alphabetic, then you need to use LIMIT and so just do the following.

select @rownum:=@rownum+1 as naturalorder, * from foo, (SELECT @rownum:=0) nat order by naturalorder desc limit 1;

but warning that there is no guarantee from mysql on the order of the records. so you might want to add an extra field with a timestamp fields or an auto_increment which will have the order that you are looking for, i think.

If it is alphabetical, the trick is to order by the code descending and then get the 1st record. And you can limit that by one.

select num, code from thetable order by code DESC limit 1

if you use group by, you have to scan through the entire table. and also it's difficult to get the full record.