I have 2 questions. First of all I have a MySQL Database with the rows: id(AUTO_INCREMENT PRIMARY KEY), name and time. This database represents the times of a race. I would like to select the name and time where the time is the smallest.
SELECT name, MIN(time) as time FROM race GROUP BY TIME;
This query gives me all times and names as long as there are no duplicates in the names. I however only want the fastest time and the name in that row.
Then when I submit my time i would like to know on what place I am. Will ORDER BY TIME keep each ID of each row the same or can I just ORDER table BY time and then select row where ID= 1?
If it's possible to have multiple entries with the same time, I would use a nested query like this, because limiting the result set to 1 may exclude a name.
select name, time from race where time = (select min(time) from race)
If you want to know what place a given time is in, just count the number of entries that have times less than it.
select count(*) + 1 as place from race where time < [your time]
For your first question, what you want is to select the 'least' time.
Here is, what I think, the clearest way to do that, which uses the LIMIT function to only return 1 row.
MySQL:
SELECT name, time
FROM race
ORDER BY time asc
LIMIT 1;
MS SQL:
SELECT TOP 1 name, time
FROM race
ORDER BY time asc
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
I have been looking on the web on how to select a random row on big tables, I have found various results, but then I analyzed my data and figured out that the best way for me to go is to count the rows and select a random one of those with LIMIT
While testing I start to wonder why this works:
SET #t = CEIL(RAND()*(SELECT MAX(id) FROM logo));
SELECT id
FROM logo
WHERE
current_status_id=29 AND
logo_type_id=4 AND
active='y' AND
id>=#t
ORDER BY id
LIMIT 1;
and gives random results, but this always returns the same 4 or 5 results ?
SELECT id
FROM logo
WHERE
current_status_id=29 AND
logo_type_id=4 AND
active='y' AND
id>=CEIL(RAND()*(SELECT MAX(id) FROM logo))
ORDER BY id
LIMIT 1;
the table has MANY fields (almost 100) and quite a few indexes. over 14 Million records and counting. When I select a random it is almost NEVER that I have to select it from the table, I always have to select depending on various fields values (all indexed).
Could it be a bug of my MySQL server version (5.6.13-log Source distribution)?
One possibility is that this statement in the documentation:
RAND() in a WHERE clause is re-evaluated every time the WHERE is executed.
is simply not always true. It is true when you do:
where rand() < 0.01
to get an approximate 1% sample of the rows. Perhaps the MySQL optimizer says something like "Oh, I'll evaluate the subquery to get one value back. And, just to be more efficient, I'll multiply that row by rand() before defining the constant."
If I had to guess, that would be the case.
Another possibility is that the data is arranged so the values you are looking for has one row with a large id. Or, it could be that there are lots of rows with small ids at the very beginning, and then a very large gap.
Your method of getting a random row, by the way is not guaranteed to return a result when you are doing filtering. I don't know if that is important to you.
EDIT:
Check to see if this version works as you expect:
SELECT id
FROM logo cross join
(SELECT MAX(id) as maxid FROM logo) c
WHERE current_status_id = 29 AND
logo_type_id = 4 AND
active = 'y' AND
id >= RAND() * maxid
ORDER BY id
LIMIT 1;
If so, the problem is that the max id is being calculated and then there is an extra step of multiplying it by rand() as execution of the query begins.
This might be a simple one, but since I don't have much knowledge about MySQL I don't know how to do this, This is what I basically want,
I have a query like this
//time format "yyyy-MM-dd"
SELECT ID
FROM `id_table`
WHERE time > "2012-01-05 " AND time < "2012-01-10";
But in the id_table I have data only up to 2012-01-04 then it starts again from "2012-01-20", so above query would return null. Is there a any way where I can retrieve the last data record from the table, as for this example can I get the ID of 2012-01-04 date from the table when I query like this
SELECT ID
FROM `id_table`
WHERE time > "2012-01-05"
Are you looking for the one (i assume max ID) ID of the row with the nearest time to 2010-01-05?
SELECT MAX(ID) as LastId FROM id_table
WHERE time = (SELECT MAX(time)
FROM id_table WHERE time < '2012-01-05')
Try this:
SELECT ID FROM id_table
WHERE time between
least((select max(time) from id_table), "2012-01-05") AND "2012-01-10";
Note that between will get data from "2012-01-10" and ("2012-01-05" OR "2012-01-05)
To get the record closest to the given time ( you could easily tweak this if you care about dealing with duplicates, if that doesn't matter then this alone should suffice)
SELECT
ID
FROM
id_table
ORDER BY ABS(DATEDIFF(time, '2012-01-05'))
LIMIT 1
NOTE: If the time field is a time value yyyy-mm-dd hh:mm:ss then you can use TIMEDIFF for a more accurate comparison.
OP If you will explain more on how you would like to handle different cases I can tweak this example to suit them. Cheers.
I have a time log table where all entries are entered with a time stamp and an event.
Now I want to select all the rows after a specific event AND ONE row before(ORDER BY time_stamp) that event.
I can easily achieve this with multiple queries, but is it possible with only one query ?
Using multiple queries
SELECT time
FROM table
WHERE event LIKE '%event_to_fint%'
SELECT event
FROM table
WHERE time<'time from last query'
LIMIT 1
ORDER BY
time DESC
One option is to
Use a regular select to select the time records you need.
Union this result with a select that retrieves the maximum time where this maximum time is less than the minimum time from your regular select.
SQL Statement
SELECT time
FROM table
WHERE event LIKE '%event_to_fint%'
UNION ALL
SELECT MAX(time)
FROM table
WHERE time < (
SELECT MIN(time)
FROM table
WHERE event LIKE '%event_to_fint%'
)
This solution in not too nice, but works:
SELECT *
FROM table
WHERE <condition_A>
ORDER BY <condition_B>
LIMIT (SELECT COUNT(*)
FROM table
WHERE <condition_A>
)+1
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