I'm very sorry if the question seems too basic.
I've surfed entire Internet and StackOverflow for a finished solution, and did not find anything that I can understand, and can't write it myself, so have to ask it here.
I have a MySQL database.
It has a table named "posted".
It has 8 columns.
I need to output this result:
SELECT DISTINCT link FROM posted WHERE ad='$key' ORDER BY day, month
But I need not only the "link" column, but also other columns for this row.
Like for every row returned with this query I also need to know its "id" in the table, "day" and "month" values etc.
Please tell me what should I read to make it, or how to make it.
Please keep it as simple as possible, as I'm not an expert in MySQL.
Edit:
I tried this:
SELECT DISTINCT link,id,day,month FROM posted WHERE ad='$key' ORDER BY day, month
It doesn't work. It returns too many rows. Say there are 10 rows with same links, but different day/month/id. This script will return all 10, and I want only the first one (for this link).
The problem comes from instinctively believing that DISTINCT is a local pre-modifier for a column.
Hence, you "should" be able to type
XXbadXX SELECT col1, DISTINCT col2 FROM mytable XXbadXX
and have it return unique values for col2. Sadly, no. DISTINCT is actually a global post-modifier for SELECT, that is, as opposed to SELECT ALL (returning all answers) it is SELECT DISTINCT (returning all unique answers). So a single DISTINCT acts on ALL the columns that you give it.
This makes it real hard to use DISTINCT on a single column, while getting the other columns, without doing major extremely ugly backflips.
The correct answer is to use a GROUP BY on the columns that you want to have unique answers: SELECT col1, col2 FROM mytable GROUP BY col2 will give you arbitrary unique col2 rows, with their col1 data as well.
I tried this:
SELECT DISTINCT link,id,day,month FROM posted
WHERE ad='$key' ORDER BY day, month
It doesn't work. It returns too many rows. Say there are 10 rows with
same links, but different day/month/id. This script will return all
10, and I want only the first one (for this link).
What you're asking doesn't make sense.
Either you want the distinct value of all of link, id, day, month, or you need to find a criterion to choose which of the values of id, day, month you want to use, if you just want at most one distinct value of link.
Otherwise, what you're after is similar to MySQL's hidden columns in GROUP BY/HAVING statements, which is non-standard SQL, and can actually be quite confusing.
You could in fact use a GROUP BY link if it made sense to pick any row for a given link value.
Alternatively, you could use a sub-select to pick the row with the minimal id for a each link value (as described in this answer):
SELECT link, id, day, month FROM posted
WHERE (link, id) IN
(SELECT link, MIN(id) FROM posted ad='$key' GROUP BY link)
SELECT Id, Link, Day, Month FROM Posted
WHERE Id IN(
SELECT Min(Id) FROM Posted GROUP BY Link)
SELECT OTHER_COLUMNS FROM posted WHERE link in (
SELECT DISTINCT link FROM posted WHERE ad='$key' )
ORDER BY day, month
If what your asking is to only show rows that have 1 link for them then you can use the following:
SELECT * FROM posted WHERE link NOT IN
(SELECT link FROM posted GROUP BY link HAVING COUNT(LINK) > 1)
Again this is assuming that you want to cut out anything that has a duplicate link.
I think the best solution would be to do a subquery and then join that to the table. The sub query would return the primary key of the table. Here is an example:
select *
from (
SELECT row_number() over(partition by link order by day, month) row_id
, *
FROM posted
WHERE ad='$key'
) x
where x.row_id = 1
What this does is the row_number function puts a numerical sequence partitioned by each distinct link that results in the query.
By taking only those row_numbers that = 1, then you only return 1 row for each link.
The way you change what link gets marked "1" is through the order-by clause in the row_number function.
Hope this helps.
SELECT DISTINCT link,id,day,month FROM posted WHERE ad='$key' ORDER BY day, month
OR
SELECT link,id,day,month FROM posted WHERE ad='$key' ORDER BY day, month
If you want all columns where link is unique:
SELECT * FROM posted WHERE link in
(SELECT link FROM posted WHERE ad='$key' GROUP BY link);
What you want is the following:
SELECT DISTINCT * FROM posted WHERE ad='$key' GROUP BY link ORDER BY day, month
if there are 4 rows for example where link is the same, it will pick only one (I asume the first one).
I had a similar problem, maybe that help someone, for example - table with 3 columns
SELECT * FROM DataTable WHERE Data_text = 'test' GROUP BY Data_Name ORDER BY Data_Name ASC
or
SELECT Data_Id, Data_Text, Data_Name FROM DataTable WHERE Data_text = 'test' GROUP BY Data_Name ORDER BY Data_Name ASC
Two ways work for me.
SELECT a.* FROM orders a INNER JOIN (SELECT course,MAX(id) as id FROM orders WHERE admission_id=".$id." GROUP BY course ) AS b ON a.course = b.course AND a.id = b.id
With the Above Query you will get unique records with where condition
In MySQL you can simply use "group by". Below will select ALL, with a DISTINCT "col"
SELECT *
FROM tbl
GROUP BY col
Select the datecolumn of month so that u can get only one row per link, e.g.:
select link, min(datecolumn) from posted WHERE ad='$key' ORDER BY day, month
Good luck............
Or
u if you have date column as timestamp convert the format to date and perform distinct on link so that you can get distinct link values based on date instead datetime
Related
So I have this data set (down below) and I'm simply trying to gather all data based on records in field 1 that have a count of more than 30 (meaning a distinct brand that has 30+ record entries) that's it lol!
I've been trying a lot of different distinct, count esc type of queries but I'm falling short. Any help is appreciated :)
Data Set
By using GROUP BY and HAVING you can achieve this. To select more columns remember to add them to the GROUP BY clause as well.
SELECT Mens_Brand FROM your_table
WHERE Mens_Brand IN (SELECT Mens_Brand
FROM your_table
GROUP BY Mens_Brand
HAVING COUNT(Mens_Brand)>=30)
You can simply use a window function (requires mysql 8 or mariadb 10.2) for this:
select Mens_Brand, Mens_Price, Shoe_Condition, Currency, PK
from (
select Mens_Brand, Mens_Price, Shoe_Condition, Currency, PK, count(1) over (partition by Mens_Brand) brand_count
from your_table
) counted where brand_count >= 30
My database is called: (training_session)
I try to print out some information from my data, but I do not want to have any duplicates. I do get it somehow, may someone tell me what I do wrong?
SELECT DISTINCT athlete_id AND duration FROM training_session
SELECT DISTINCT athlete_id, duration FROM training_session
It works perfectly if i use only one column, but when I add another. it does not work.
I think you misunderstood the use of DISTINCT.
There is big difference between using DISTINCT and GROUP BY.
Both have some sort of goal, but they have different purpose.
You use DISTINCT if you want to show a series of columns and never repeat. That means you dont care about calculations or group function aggregates. DISTINCT will show different RESULTS if you keep adding more columns in your SELECT (if the table has many columns)
You use GROUP BY if you want to show "distinctively" on a certain selected columns and you use group function to calculate the data related to it. Therefore you use GROUP BY if you want to use group functions.
Please check group functions you can use in this link.
https://dev.mysql.com/doc/refman/8.0/en/group-by-functions.html
EDIT 1:
It seems like you are trying to get the "latest" of a certain athlete, I'll assume the current scenario if there is no ID.
Here is my alternate solution:
SELECT a.athlete_id ,
( SELECT b.duration
FROM training_session as b
WHERE b.athlete_id = a.athlete_id -- connect
ORDER BY [latest column to sort] DESC
LIMIT 1
) last_duration
FROM training_session as a
GROUP BY a.athlete_id
ORDER BY a.athlete_id
This syntax is called IN-SELECT subquery. With the help of LIMIT 1, it shows the topmost record. In-select subquery must have 1 record to return or else it shows error.
MySQL's DISTINCT clause is used to filter out duplicate recordsets.
If your query was SELECT DISTINCT athlete_id FROM training_session then your output would be:
athlete_id
----------
1
2
3
4
5
6
As soon as you add another column to your query (in your example, the column called duration) then each record resulting from your query are unique, hence the results you're getting. In other words the query is working correctly.
I searched for an answer here and didn't find one closer to my question.
I have the following situation: I need to display a person first and then show the rest in ascending order. All the people from the same table. I tried UNION but after that, the SQL seems to mix everything again.
I have tried this:
select name from people where name = 'John'
UNION
select name from people order by name
Since UNION does not select duplicated values. But in the end, it mixed up every result and did not show in the correct order that should be:
John
Ana
Bruce
What am I doing wrong?
You need to use order by to get what you want. In MySQL, this is pretty easy:
select name
from people
order by (name = 'John') desc, name
Results sets (like tables) represent unordered sets in SQL. The only way to impose an order is to use order by. The order by at the end of a union/union all query applies to the entire query.
As an aside, your code would come close to working if you used union all -- which is much preferred over union. The union operation does additional work to remove duplicates. In this case, that reorders the results, a convenient reminder that you can only depend on the order of results when you use order by.
Also you can use UNION ALL in a derived table
SELECT name
FROM
(
SELECT 1 AS Row_Id, name
FROM people
WHERE name = 'John'
UNION ALL
SELECT 2 AS Row_Id, name
FROM people
) t
ORDER BY Row_Id
I have a table about how often an event occurs, and I want to see first and last occurrence of every event. Assume I have three columns, event_id, event_time and event_date. I know queries like this are wrong, and give false result:
SELECT
event_id,
MIN(event_time),
MAX(event_time),
MIN(event_date),
MAX(event_date)
FROM events_table
WHERE 1
GROUP BY event_id
Is there any way I could do this without merging two columns?
Please be more precisely regarding column types (date,time,varchar..) and if you would look for occurence of the event by day or ever.
You can just concatenate these two columns and min,max it.
Following assumes event_time like '08:03:21' and event_date('2014-01-30') occurence ever:
SELECT id, event_id, min(concat(event_date,' ',event_time)),max(concat(event_date,' ',event_time))
from t_test
group by event_id
If you would like to check the first,last occurence per day, just group by day and remove the date from concat().
You forgot FROM
Here is another approach. Tested on my MySQL
SELECT a1.event_id,
Min(Concat(a2.event_date, ' ', a2.event_time)),
Max(Concat(a2.event_date, ' ', a2.event_time))
FROM event_log a1
INNER JOIN event_log a2
ON a2.event_id = a1.event_id
GROUP BY a1.event_id
This simple SQL problem is giving me a very hard time. Either because I'm seeing the problem the wrong way or because I'm not that familiar with SQL. Or both.
What I'm trying to do: I have a table with several columns and I only need two of them: the datetime when the entry was created and the id of the entry. Note that the hours/minutes/seconds part is important here.
However, I want to group my selection according to the DATE part only. Otherwise all groups will most likely have 1 element.
Here's my query:
SELECT MyDate as DateCr, COUNT(Id) as Occur
FROM MyTable tb WITH(NOLOCK)
GROUP BY CAST(tb.MyDate as Date)
ORDER BY DateCr ASC
However I get the following error from it:
Column "MyTable.MyDate" is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
If I don't do the cast in the GROUP BY, everything fine. If I cast MyDate to DATE in the SELECT and keep the CAST from GROUP BY, everything fine once more. Apparently it wants to keep the same DATE or DATETIME format in the GROUP BY as in the SELECT.
My approach can be completely wrong so I am not necessarily looking to fix the above query, but to find the proper way to do it.
LE: I get the above error on line 1.
LE2: On a second look, my question indeed is not very explicit. You can ignore the above approach if it is completely wrong. Below is a sample scenario
Let me tell you what I need: I want to retrieve (1) the DateTime when each entry was created. So if I have 20 entries, then I want to get 20 DateTimes. Then if I have multiple entries created on the same DAY, I want the number of those entries. For example, let's say I created 3 entries on Monday, 1 on Tuesday and 2 today. Then from my table I need the datetimes of these 6 entries + the number of entries which were created on each day (3 for 19/03/2012, 1 for 20/03/2012 and 2 for 21/03/2012).
I'm not sure why you're objecting to performing the CONVERT in both the SELECT and the GROUP BY. This seems like a perfectly logical way to do this:
SELECT
DateCr = CONVERT(DATE, MyDate),
Occur = COUNT(Id)
FROM dbo.MyTable
GROUP BY CONVERT(DATE, MyDate)
ORDER BY DateCr;
If you want to keep the time portion of MyDate in the SELECT list, why are you bothering to group? Or how do you expect the results to look? You'll have a row for every individual date/time value, where the grouping seems to indicate you want a row for each day. Maybe you could clarify what you want with some sample data and example desired results.
Also, why are you using NOLOCK? Are you willing to trade accuracy for a haphazard turbo button?
EDIT adding a version for the mixed requirements:
;WITH d(DateCr,d,Id) AS
(
SELECT MyDate, d = CONVERT(DATE, MyDate), Id
FROM dbo.MyTable)
SELECT DateCr, Occur = (SELECT COUNT(Id) FROM d AS d2 WHERE d2.d = d.d)
FROM d
ORDER BY DateCr;
Even though this is an old post, I thought I would answer it. The solution below will work with SQL Server 2008 and above. It uses the over clause, so that the individual lines will be returned, but will also count the rows grouped by the date (without time).
SELECT MyDate as DateCr,
COUNT(Id) OVER(PARTITION BY CAST(tb.MyDate as Date)) as Occur
FROM MyTable tb WITH(NOLOCK)
ORDER BY DateCr ASC
Darren White