I want to count the ugyfel_email field in this select.
If i run it, i didnt get errors, but from the table records, it will only show one row.
What am i doing wrong?
SELECT id,ugyfel_nev,ugyfel_email,parkolo_tipus,ugyfel_tel,rendszam,erkezes_datum,
erkezes_ideje,allapot, utasok, COUNT(ugyfel_nev) AS ennyiszer FROM foglalas WHERE allapot = 'Feldolgozva' ORDER BY id DESC
In order to count a column, you need to reference it to some other column. By that I mean it needs to represent something. In your query I assume you want to count how many ugyfel_emain there is for a specific allpot, this will look like:
SELECT COUNT(ugyfel_nev), COUNT(ugyfel_email)
FROM foglalas
GROUP BY allapot
HAVING allapot = 'Feldolgozva' # if you want only for this
ORDER BY id DESC
Related
I am trying to do a simple test where I'm pulling from a table the information of a specific part number as such:
SELECT *
FROM table_name
WHERE part_no IN ('abc123')
This returns 25 rows. Now I want to count the number that meet the "accepted" condition in a specific column but the result is limited to only the 10 most recent. My approach is to write it as follows:
Select Count(*)
FROM table_name
WHERE part_no IN ('abc123') AND lot IN ('accepted')
ORDER BY date DESC
LIMIT 10
I'm having a hard time to get the ORDER BY and LIMIT operations to work. I could use help just getting it to limit appropriately, and I can figure out the rest from there.
Edit: I understand that the operations are happening on the COUNT which only returns one row with a value; but I put the second clip to show where I am stuck in my thought process.
Your query SELECT Count(*) FROM ... will always return exactly one row.
It's not 100% clear what exactly you want to do, but if you want to know how many of the last 10 have been accepted, you could use a subquery - something like:
SELECT COUNT(*) FROM (
SELECT lot
FROM table_name
WHERE part_no IN ('abc123')
ORDER BY date DESC
LIMIT 10
)
WHERE lot IN ('accepted')
The inner query will return the 10 most recent rows for part abc123, then the outer query will count the accepted ones.
There are also other solution (for example, you could have the inner query output a field that is 0 when the part is not accepted and 1 when the part is accepted, then take the sum). Depending on which exact dialect/database you are using, you may also have more elegant options.
Select count returns ONE ROW therefore the ORDER BY and the LIMIT will not work on the results
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 have an EAV table in SQL which as usual has several records for each ID. Each of these records has a numerical value in a column called 'weight' and I'm trying to sort this table so that for each ID the records are ranked in descending order of weight. This is going to be a one off process because I intend to make sure that data is sorted when it goes into the table in future.
Also is the normal protocol for doing something like this to SELECT all of the data, sort it the way you want, and then use the REPLACE command to replace the old data in the table?
I know that I can do this for one id by doing:
SELECT * FROM my_table WHERE id = 'X' ORDER BY weight DESC
but I need to somehow do this for each id in my table. How is this normally done?
you will ALWAYS return the data in the order you wish in this case:
SELECT * from theTable order by id, weight desc
you do not store the data in any particular order. (even if you try this will not matter).
Remove the WHERE clause and add id to ORDER BY. This way, your result set will be ordered first by id, and for each id, it will be ordered by weight.
SELECT * FROM my_table ORDER BY id, weight DESC
why is this query giving weird results..
SELECT max(greatest(home_team_total,away_team_total)) AS max_team_score, id
FROM `match`
WHERE id IN (1,2,3,4,5)
while
SELECT greatest(home_team_total,away_team_total) AS max_team_score, id
FROM `match`
WHERE id IN (1,2,3,4,5)
ORDER BY max_team_score DESC
LIMIT 1
gives correct result..
The max value is correct only in both cases but id of match is wrong in first case..
It's because you're including the id field in the SELECT clause. Which id do you want? I get that you might want the one associated with the max row, but there could be multiple ones, and what if you were also returning min(greatest(home_team_total,away_team_total))?
The second query is the one you want for this problem.
Editing to make it a little clearer:
Your query is equivalent to:
SELECT max(greatest(home_team_total,away_team_total)) AS max_team_score, ANY(id)
FROM `match`
WHERE id IN (1,2,3,4,5)
Look at http://dev.mysql.com/doc/refman/5.0/en/group-by-hidden-columns.html
It says: "The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate."
If you do want the first query to work, you have to change it to something like the following:
SELECT greatest(home_team_total,away_team_total) AS max_team_score, id
FROM match
WHERE greatest(home_team_total,away_team_total) =
(
SELECT max(greatest(home_team_total,away_team_total)) FROM match
)
Note that you can have more than one row in the result, so I would prefer this solution to the "LIMIT 1" alternative.
What's the most efficient way to select the last n number of rows in a table using mySQL? The table contains millions of rows, and at any given time I don't know how large the table is (it is constantly growing). The table does have a column that is automatically incremented and used as a unique identifier for each row.
SELECT * FROM table_name ORDER BY auto_incremented_id DESC LIMIT n
Actually the right way to get last n rows in order is to use a subquery:
(SELECT id, title, description FROM my_table ORDER BY id DESC LIMIT 5)
ORDER BY tbl.id ASC
As this way is the only I know that will return them in right order. The accepted answer is actually a solution for "Select first 5 rows from a set ordered by descending ID", but that is most probably what you need.
(Similar to "marco"s answer,)
my fav is the max()-function of MySQL too, in a simple one-liner, but there are other ways of sure:
SELECT whatever FROM mytable WHERE id > (SELECT max(id)-10 FROM mytable);
... and you get "last id minus 10", normally the last 10 entries of that table.
It's a short way, to avoid the a error 1111 ("Invalid use of group function") not only if there is a auto_increment-row (here id).
The max()-function can be used many ways.
Maybe order it by the unique id descending:
SELECT * FROM table ORDER BY id DESC LIMIT n
The only problem with this is that you might want to select in a different order, and this problem has made me have to select the last rows by counting the number of rows and then selecting them using LIMIT, but obviously that's probably not a good solution in your case.
Use ORDER BY to sort by the identifier column in DESC order, and use LIMIT to specify how many results you want.
You would probably also want to add a descending index (or whatever they're called in mysql) as well to make the select fast if it's something you're going to do often.
This is a lot faster when you have big tables because you don't have to order an entire table.
You just use id as a unique row identifier.
This is also more eficient when you have big amounts of data in some colum(s) as images for example (blobs). The order by in this case can be very time and data consuming.
select *
from TableName
where id > ((select max(id) from TableName)-(NumberOfRowsYouWant+1))
order by id desc|asc
The only problem is if you delete rows in the interval you want. In this case you would't get the real "NumberOfRowsYouWant".
You can also easily use this to select n rows for each page just by multiplying (NumberOfRowsYouWant+1) by page number when you need to show the table backwards in multiple web pages.
Here you can change table name and column name according your requirement . if you want to show last 10 row then put n=10,or n=20 ,or n=30 ...etc according your requirement.
select * from
(select * from employee
Order by emp_id desc limit n)
a Order by emp_id asc;