the "t_example" table :
id | date
---------------
1 | 2001-05-09
1 | 2005-11-05
1 | 2000-08-19
2 | 2010-10-30
2 | 2002-12-10
2 | 2009-07-29
3 | 2003-02-15
3 | 2012-04-20
I would like to create a view that returns the following result (the max date for each id):
id | date_id
---------------
1 | 2005-11-05
2 | 2010-10-30
3 | 2012-04-20
MySQL don't allow to do a subquery with order by in view, and when I use an other view for the subquery, the group by ignore the order by in the subquery.
The following query returns the expected result:
select id, date
from (select id, date from t_example order by id asc, date_id desc) p
group by p.id
But when I use it in a views it does't work:
view1 (subquery) : select id, date from t_example order by id asc, date_id desc;
view2 : select id, date from view1 group by view1.id;
Is there any other solution?
This should work for you
SELECT id, MAX(date) AS date FROM t_example GROUP BY id;
This is using the AS syntax to keep your column name succinct (otherwise it would be MAX(date))
select id,max(date)
from your_table
group by id
Related
Lets say we have a table that looks like this:
+---------------+----------------+-------------------+
| ID | random_string | time |
+---------------+----------------+-------------------+
| 2 | K2K3KD9AJ |2022-07-21 20:41:15|
| 1 | SJQJ8JD0W |2022-07-17 23:46:13|
| 1 | JSDOAJD8 |2022-07-11 02:52:21|
| 3 | KPWJOFPSS |2022-07-11 02:51:57|
| 1 | DA8HWD8HHD |2022-07-11 02:51:49|
------------------------------------------------------
I want to select the last 3 entries into the table, however they must all have separate ID's.
Expected Result:
+---------------+----------------+-------------------+
| ID | random_string | time |
+---------------+----------------+-------------------+
| 2 | K2K3KD9AJ |2022-07-21 20:41:15|
| 1 | SJQJ8JD0W |2022-07-17 23:46:13|
| 3 | KPWJOFPSS |2022-07-11 02:51:57|
------------------------------------------------------
I have already tried:
SELECT DISTINCT id FROM table ORDER BY time DESC LIMIT 3;
And:
SELECT MIN(id) as id FROM table GROUP BY time DESC LIMIT 3;
If you're not on MySQL 8, then I have two suggestions.
Using EXISTS:
SELECT m1.ID,
m1.random_string,
m1.time
FROM mytable m1
WHERE EXISTS
(SELECT ID
FROM mytable AS m2
GROUP BY ID
HAVING m1.ID=m2.ID
AND m1.time= MAX(time)
)
Using JOIN:
SELECT m1.ID,
m1.random_string,
m1.time
FROM mytable m1
JOIN
(SELECT ID, MAX(time) AS mxtime
FROM mytable
GROUP BY ID) AS m2
ON m1.ID=m2.ID
AND m1.time=m2.mxtime
I've not test in large data so don't know which will perform better (speed) however this should return the same result:
Here's a fiddle
Of course, this is considering that there will be no duplicate of exact same ID and time value; which seems to be very unlikely but still it's possible.
Using MySql 8 an easy solution is to assign a row number using a window:
select Id, random_string, time
from (
select *, Row_Number() over(partition by id order by time desc) rn
from t
)t
where rn = 1
order by time desc
limit 3;
See Demo
I am a SQL beginner and am learning the ropes of querying. I'm trying to find the date difference between purchases by the same customer. I have a dataset that looks like this:
ID | Purchase_Date
==================
1 | 08/10/2017
------------------
1 | 08/11/2017
------------------
1 | 08/17/2017
------------------
2 | 08/09/2017
------------------
3 | 08/08/2017
------------------
3 | 08/10/2017
I want to have a column that shows the difference in days for each unique customer purchase, so that the output will look like this:
ID | Purchase_Date | Difference
===============================
1 | 08/10/2017 | NULL
-------------------------------
1 | 08/11/2017 | 1
-------------------------------
1 | 08/17/2017 | 6
-------------------------------
2 | 08/09/2017 | NULL
-------------------------------
3 | 08/08/2017 | NULL
-------------------------------
3 | 08/10/2017 | 2
What would be the best way to go about this using a MySQL query?
Not so hard, just use a subquery to find previous purchase for each existing purchase for the customer, and self-join to that record.
Select t.id, t.PurchaseDate, p.Purchase_date,
DATEDIFF(t.PurchaseDate, p.Purchase_date) Difference
From myTable t -- t for This purchase record
left join myTable p -- p for Previous purchase record
on p.id = t.Id
and p.purchase_date =
(Select Max(purchase_date)
from mytable
where id = t.id
and purchase_date <
t.purchaseDate)
This is rather tricky in MySQL. Probably the best way to learn if you are a beginning is the correlated subquery method:
select t.*, datediff(purchase_date, prev_purchase_date) as diff
from (select t.*,
(select t2.purchase_date
from t t2
where t2.id = t.id and
t2.purchase_date < t.purchase_date
order by t2.purchase_date desc
limit 1
) as prev_purchase_date
from t
) t;
Performance should be okay if you have an index on (id, purchase_date).
It is possible to solve it not using dependent subquery
SELECT yt.id, create_date, NULLIF(yt.create_date - tm.min_create_date, 0)
FROM your_table yt
JOIN
(
SELECT id, MIN(create_date) min_create_date
FROM your_table
GROUP BY id
) tm ON tm.id = yt.id
sqlfiddle demo
How can I select one row only in same ID?
This is my MySQL Code
Select * from logoutdetails ORDER BY LogInTime DESC LIMIT 1;
This is my Table
--------------------------------
| ID | LogInTime |
--------------------------------
| 07 | 2017-01-25 14:41:32 |
| 08 | 2017-01-25 14:33:22 |
| 07 | 2017-01-25 14:26:28 |
| 08 | 2017-01-25 14:18:56 |
--------------------------------
If you are satisfied with taking the most recent timestamp from each ID then you can try this:
SELECT ID, MAX(LogInTime) AS LogInTime
FROM logoutdetails
GROUP BY ID
ORDER BY ID
You could also use MIN() in place of MAX(), if you wanted to retain the earliest login time.
If the logoutdetails table had other columns and you wanted to select those too, you would have to use a subquery to first identify the maximum ID records and then join back to your original table. Something like this:
SELECT t1.*
FROM logoutdetails t1
INNER JOIN
(
SELECT ID, MAX(LogInTime) AS max_login_time
FROM logoutdetails
GROUP BY ID
) t2
ON t1.ID = t2.ID AND
t1.LogInTime = t2.max_login_time
Group by the id to get only unique ones. Then you have to decide which date you want to get for each id. Use max() to get the latest date for each
Select id, max(LogInTime) as LogInTime
from logoutdetails
group by id
I have a table called tbl_user_sal:
| id | user_id | salary | date |
| 1 | 1 | 1000 | 2014-12-01 |
| 2 | 1 | 2000 | 2014-12-02 |
Now I want to get the id of the maximum date. I used the following query:
SELECT MAX(date) AS from_date, id, user_id, salary
FROM tbl_user_sal
WHERE user_id = 1
But it gave me this output:
| id | user_id | salary | from_date |
| 1 | 1 | 2000 | 2014-12-02 |
Which is correct as far as the max date being 2014-12-02, but the corresponding id is not correct. This happens for other records as well. I used order by to check but that was not successful either. Can anyone shed some light on this?
Note: Its not necessary that max date will have max id, according to my needs. Records can have max date but id may be older.
If you only want to retrieve that information for a single user, which you seem to, because of your WHERE clause, just use ORDER BY and LIMIT:
SELECT *
FROM tbl_user_sal
WHERE user_id = 1
ORDER BY date DESC
LIMIT 1
If you want to do that for every user, however, you will have to get a little bit fancier. Something like that should do it:
SELECT t2.id, user_id, date
--find max date for each user_id
FROM (SELECT user_id, MAX(date) AS date
FROM tbl_user_sal
GROUP BY user_id) AS t1
--join ids for each max date/user_id combo
JOIN tbl_user_sal AS t2
USING (user_id, date)
--limit to 1 id for every user_id
GROUP BY
user_id
You are missing group by clause Try this:
select max(awrd_date) as from_date,awrd_id
from tbl_user_sal
where awrd_user_id = 106
group by awrd_id
What I believe you should do here is have a subquery that pulls the max date, and your outer query looks for the row with that date.
It looks like this:
SELECT *
FROM myTable
WHERE date = (SELECT MAX(date) FROM myTable);
Additional things may need to be added if you want to search for a specific user_id, or get the largest date for each user_id, but this gives your expected results for this example here.
Here is the SQL Fiddle.
I have read that grouping happens before ordering, is there any way that I can order first before grouping without having to wrap my whole query around another query just to do this?
Let's say I have this data:
id | user_id | date_recorded
1 | 1 | 2011-11-07
2 | 1 | 2011-11-05
3 | 1 | 2011-11-06
4 | 2 | 2011-11-03
5 | 2 | 2011-11-06
Normally, I'd have to do this query in order to get what I want:
SELECT
*
FROM (
SELECT * FROM table ORDER BY date_recorded DESC
) t1
GROUP BY t1.user_id
But I'm wondering if there's a better solution.
Your question is somewhat unclear but I have a suspicion what you really want is not any GROUP aggregates at all, but rather ordering by date first, then user ID:
SELECT
id,
user_id,
date_recorded
FROM tbl
ORDER BY date_recorded DESC, user_id ASC
Here would be the result. Note reordering by date_recorded from your original example
id | user_id | date_recorded
1 | 1 | 2011-11-07
3 | 1 | 2011-11-06
2 | 1 | 2011-11-05
5 | 2 | 2011-11-06
4 | 2 | 2011-11-03
Update
To retrieve the full latest record per user_id, a JOIN is needed. The subquery (mx) locates the latest date_recorded per user_id, and that result is joined to the full table to retrieve the remaining columns.
SELECT
mx.user_id,
mx.maxdate,
t.id
FROM (
SELECT
user_id,
MAX(date_recorded) AS maxdate
FROM tbl
GROUP BY user_id
) mx JOIN tbl t ON mx.user_id = t.user_id AND mx.date_recorded = t.date_recorded
Iam just using the technique
"Using order clause before group by inserting it in group_concat clause"
SELECT SUBSTRING_INDEX(group_concat(cast(id as char)
ORDER BY date_recorded desc),',',1),
user_id,
SUBSTRING_INDEX(group_concat(cast(`date_recorded` as char)
ORDER BY `date_recorded` desc),',',1)
FROM data
GROUP BY user_id