How can I get unique rows from a mysql table based on value of one column?(See below the screenshot, I want to get unique rows of this table based on entry_id field)
I want a query which will produce following result.
----------------------
entry_id | comment_id
----------------------
380 4716
371 4723
FYI, table name is comments. (My goal is to get latest comment(last one) for each entries). I'm aware that this can't be achieved using DISTINCT or group by.
Appreciate your help. Thanks
If you want to select only entry_id:
SELECT DISTINCT entry_id FROM table WHERE ...
Or if you need select many columns you should do that:
SELECT entry_id, comment_id ... FROM table WHERE ... GROUP BY entry_id
Following query served my purpose(If somebody face similar issue)
SELECT entry_id, MAX(comment_id) AS comment_id FROM comments GROUP BY `entry_id`
Try this query :
select entry_id ,
(select comment_id from comments t1
where t1.entry_id= t2.entry_id
order by comment_id desc
limit 1) 'comment_id'
from comments t2;
Related
I have the following table structure:
Request table:
id insret_time account id
------------------------------------
1 2018-04-05 08:06:23 abc
2 2018-09-03 08:14:45 abc
3 2018-08-13 09:23:34 xyz
4 2018-08-04 09:25:37 def
5 2018-08-24 11:45:37 def
I need to find the latest records for account IDs abc and def. I don't care about xyz.
I tried to get the results using group by and inner join methods but was not successful in limiting the results to just the user list I care about.
Please advice
Update:
Thanks everyone for your feedback. Appreciate it! I needed the entire row as the output. I have used id column instead of timestamp to get the latest record since its auto-incremented This is what I finally came up with that gave me the output I need:
select t.* FROM table t
join (select max(table.id) as maxNum from table
where account_id in ('abc','def') group by account_id) tm on t.id = tm.maxNum;
I think this is what you were looking for
select account_id,max(insret_time)
from table where account_id in ('abc', 'def')
group by account_id
You can use not in and ignore xyz records and placing order by desc:
select account_id,max(insert_time) from table where account_id not in ('xyz') group by account_id order by id desc
Also you can use != operators just for one expression:
select account_id,max(insert_time) from table where account_id!='xyz' group by account_id order by id desc
I hope it helps :)
Using PHP and MySQL, I want to query a table of postings my users have made to find the person who has posted the most entries.
What would be the correct query for this?
Sample table structure:
[id] [UserID]
1 johnnietheblack
2 johnnietheblack
3 dannyrottenegg
4 marywhite
5 marywhite
6 johnnietheblack
I would like to see that "johnnietheblack" is the top poster, "marywhite" is second to best, and "dannyrottenegg" has the least
Something like:
SELECT COUNT(*) AS `Rows`, UserID
FROM `postings`
GROUP BY UserID
ORDER BY `Rows` DESC
LIMIT 1
This gets the number of rows posted by a particular ID, then sorts though the count to find the highest value, outputting it, and the ID of the person. You'll need to replace the 'UserID' and 'postings' with the appropriate column and field though.
I believe this should work...
SELECT user_id, COUNT(*) FROM postings ORDER BY COUNT(*) GROUP BY user_id LIMIT 1
Assuming posting is a tuple (user_id, recipient_user_id), where each row represents one posting, from user_id to recipient_user_id:
select user_id, count(*) as posts
from postings
group by user_id
having count(*) = max(count(*)) ;
I have a table in a MySQL database with an ID column. This is not a key of the table and several rows can have the same ID.
I don't really know SQL but I already figured out how to obtain the number of distinct IDs:
SELECT COUNT(DISTINCT ID) FROM mytable;
Now I want to count only those IDs which appear more than 2 times in the table.
So if the ID column contains the values
3 4 4 5 5 5 6 7 7 7
the query should return 2.
I have no idea how to do this. I hope someone can help me!
Btw, my table contains a huge number of rows. So if there are several possibilities I would also be happy to know which solution is the most efficient.
Try this:
SELECT COUNT(ID) FROM (
SELECT ID FROM mytable
GROUP BY ID
HAVING COUNT(ID) > 2) p
select count(*) from
(select count(id) as cnt,id from mytable group by id) da
where da.cnt>2
The inner query will give you how many elements does each id have. And the outer query will filter this.
SELECT
COUNT(ids)
FROM
(SELECT
COUNT(ID)AS ids
FROM
mytable
GROUP BY
ID
HAVING
ids>2
)AS tbl1
Updated :
SELECT count(ID)
FROM (
SELECT ID FROM mytable
GROUP BY ID
HAVING count(ID) > 2
) p
should do what you need
I would like to determine two things from a single query:
Most prevalent column in a table
The amount of times such column was located upon querying the table
Example Table:
user_id some_field
1 data
2 data
1 data
The above would return user_id # 1 as being the most prevalent in the table, and it would return (2) for the total amount of times that it was located in the table.
I have done my research and I came across two types of queries.
GROUP BY user_id ORDER BY COUNT(*) DESC
SUM
The problem is that I can't figure out how to use these two queries in conjunction with one another. For example, consider the following query which successfully returns the most prevalent column.
$top_user = "SELECT user_id FROM table_name GROUP BY user_id ORDER BY COUNT(*) DESC";
The above query returns "1" based on the example table shown above. Now, I would like to be able to return "2" for the total amount of times the user_id (1) was found in the table.
Is this by any chance possible?
Thanks,
Evan
You can include count(*) in the SELECT list:
SELECT user_id, count(*) as totaltimes from table_name
GROUP BY user_id ORDER BY count(*) DESC;
If you want only the first one:
SELECT user_id, count(*) as totaltimes from table_name
GROUP BY user_id ORDER BY count(*) DESC LIMIT 1;
I'm currently using PHP/MySQL to select some data from my database. My current SELECT statement is:
mysql_query("SELECT * FROM tblpm WHERE receiver_id ='$usrID' GROUP BY
thread_id ORDER BY unique_id DESC") or die(mysql_error());
There are some columns that have the same "thread-id", thus, I am using the GROUP BY, so that only one "thread-id" column is selected. Everything works fine with the grouping, however, it is selecting the first 'thread-id' column, and not the most recent (which is what I want).
For example, there are 4 columns all with the same thread_id:
thread_id unique_id
222 1
222 2
222 3
222 4
When I do the GROUP BY, I would like it to retrieve the one with unique id 4 (the most recently created column), not unique id 1 (the oldest column created).
Any ideas on how to achieve this with my SELECT statement? Thanks.
SELECT thread_id, MAX(unique_id)
FROM tblpm
GROUP by thread_id
so:
mysql_query(<<<END
SELECT thread_id, MAX(unique_id)
FROM tblpm
WHERE receiver_id ='$usrID'
GROUP by thread_id
END
) or die(mysql_error());
and of course make sure you escape $usrID if it comes from the browser.
SELECT DISTINCT thread_id, unique_id
FROM tblpm
WHERE receiver_id = '$usrID'
GROUP BY thread_id
ORDER BY unique_id DESC;