I am HAVING trouble with my GROUP BY query (the trickiest of them all at least for me).
What I want to do is retrieve the most recent modified records grouped by another column. The problem as I see it is that grouping returns the only first record it finds (in the group) disregarding the ORDER BY (except when returning the final result).
Here is a simplified version of my code.
SELECT events.id, events.name, events.type, events.modified_time
FROM events
GROUP BY events.type
ORDER BY event.modified_time DESC
Which will return:
1 | Event One | Birthday | Jan 1, 2012
2 | Event Two | Graduation | Jan 1, 2012
When in fact there is a 3rd record with a modified time that is later:
3 | Event Three | Birthday | Jan 2, 2012
I've tried using a HAVING clause of MAX(modified_time) but it doesn't return the correct results either. Maybe I just need to discuss this more with someone who is knowledgeable but if the question makes enough sense and you can tell what I need then maybe there is an easy answer.
BONUS QUESTION:
Is it possible to do this without a sub query?
This, among many other methods, may work for you:
SELECT a.id, a.name, a.[type], a.modified_time
FROM [events] AS a
JOIN (
SELECT MAX([events].id) AS id, [events].[type]
FROM [events]
GROUP BY [events].[type]
) AS b ON a.id = b.id AND a.[type] = b.[type]
ORDER BY a.modified_time DESC
GROUP BY/HAVING is not what you want. What you want is either:
WHERE
events.modified_time = ( select max(modified_time) from events e2 where e2.type = events.type )
... or else a solution like Tim linked to using an analytic function like ROW_NUMBER
Related
I have very limited experience with MySQL past standard queries, but when it comes to joins and relations between multiple tables I have a bit of an issue.
I've been tasked with creating a job that will pull a few values from a mysql database every 15 minutes but the info it needs to display is pulled from multiple tables.
I have worked with it for a while to figure out the relationships between everything for the phone system and I have discovered how I need to pull everything out but I'm trying to find the right way to create the job to do the joins.
I'm thinking of creating a new table for the info I need, with columns named as:
Extension | Total Talk Time | Total Calls | Outbound Calls | Inbound Calls | Missed Calls
I know that I need to start with the extension ID from my 'user' table and match it with 'extensionID' in my 'callSession'. There may be multiple instances of each extensionID but each instance creates a new 'UniqueCallID'.
The 'UniqueCallID' field then matches to 'UniqueCallID' in my 'CallSum' table. At that point, I just need to be able to say "For each 'uniqueCallID' that is associated with the same 'extensionID', get the sum of all instances in each column or a count of those instances".
Here is an example of what I need it to do:
callSession Table
UniqueCallID | extensionID |
----------------------------
A 123
B 123
C 123
callSum table
UniqueCallID | Duration | Answered |
------------------------------------
A 10 1
B 5 1
C 15 0
newReport table
Extension | Total Talk Time | Total Calls | Missed Calls
--------------------------------------------------------
123 30 3 1
Hopefully that conveys my idea properly.
If I create a table to hold these values, I need to know how I would select, join and insert those things based on that diagram but I'm unable to construct the right query/statement.
You simply JOIN the two tables, and do a group by on the extensionID. Also, add formulas to summarize and gather the info.
SELECT
`extensionID` AS `Extension`,
SUM(`Duration`) AS `Total Talk Time`,
COUNT(DISTINCT `UniqueCallID`) as `Total Calls`,
SUM(IF(`Answered` = 1,0,1)) AS `Missed Calls`
FROM `callSession` a
JOIN `callSum` b
ON a.`UniqueCallID` = b.`UniqueCallID`
GROUP BY a.`extensionID`
ORDER BY a.`extensionID`
You can use a join and group by
select
a.extensionID
, sum(b.Duration) as Total_Talk_Time
, count(b.Answered) as Total_Calls
, count(b.Answered) -sum(b.Answered) as Missed_calls
from callSession as a
inner join callSum as b on a.UniqueCallID = b.UniqueCallID
group by a.extensionID
This should do the trick. What you are being asked to do is to aggregate the number of and duration of calls. Unless explicitly requested, you do not need to create a new table to do this. The right combination of JOINs and AGGREGATEs will get the information you need. This should be pretty straightforward... the only semi-interesting part is calculating the number of missed calls, which is accomplished here using a "CASE" statement as a conditional check on whether each call was answered or not.
Pardon my syntax... My experience is with SQL Server.
SELECT CS.Extension, SUM(CA.Duration) [Total Talk Time], COUNT(CS.UniqueCallID) [Total Calls], SUM(CASE CS.Answered WHEN '0' THEN SELECT 1 ELSE SELECT 0 END CASE) [Missed Calls]
FROM callSession CS
INNER JOIN callSum CA ON CA.UniqueCallID = CS.UniqueCallID
GROUP BY CS.Extension
I have a SELECT query that returns some fields like this:
Date | Campaign_Name | Type | Count_People
Oct | Cats | 1 | 500
Oct | Cats | 2 | 50
Oct | Dogs | 1 | 80
Oct | Dogs | 2 | 50
The query uses aggregation and I only want to include results where when Type = 1 then ensure that the corresponding Count_People is greater than 99.
Using the example table, I'd like to have two rows returned: Cats. Where Dogs is type 1 it's excluded because it's below 100, in this case where Dogs = 2 should be excluded also.
Put another way, if type = 1 is less than 100 then remove all records of the corresponding campaign name.
I started out trying this:
HAVING CASE WHEN type = 1 THEN COUNT(DISTINCT Count_People) > 99 END
I used Teradata earlier int he year and remember working on a query that used an analytic function "Qualify PartitionBy". I suspect something along those lines is what I need? I need to base the exclusion on aggregation before the query is run?
How would I do this in MySQL? Am I making sense?
Now that I understand the question, I think your best bet will be a subquery to determine which date/campaign combinations of a type=1 have a count_people greater than 99.
SELECT
<table>.date,
<table>.campaign_name,
<table>.type,
count(distinct count_people) as count_people
FROM
(
SELECT
date,
campaign_name
FROM
<table>
WHERE type=1
HAVING count(distinct count_people) > 99
GROUP BY 1,2
) type1
LEFT OUTER JOIN <table> ON
type1.campaign_name = <table>.campaign_name AND
type1.date = <table>.date
WHERE <table>.type IN (1,2)
GROUP BY 1,2,3
The subquery here only returns campaign/date combinations when both the type=1 AND it has greater than 99 count_people. It uses a LEFT JOIN back to the to insure that only those campaign/date combinations make it into the result set.
The WHERE on the main query keeps the results to only Types 1 and 2, which you stated was already a filter in place (though not mentioned in the question, it was stated in a comment to a previous answer).
Based on your comments to answer by #JNevill I think you will have no option but to use subselects to pre-filter the record set you are dealing with, as working with HAVING is going to limit you only to the current record being evaluated - there is no way to compare against previous or subsequent records in the set in this manner.
So have a look at something like this:
SELECT
full_data.date AS date,
full_data.campaign_name AS campaign_name,
full_data.type AS type,
COUNT(full_data.people) AS people_count
FROM
(
SELECT
date,
campaign_name,
type,
COUNT(people) AS people_count
FROM table
WHERE type IN (1,2)
GROUP BY date, campaign_name, type
) AS full_data
LEFT JOIN
(
SELECT
date,
campaign_name,
COUNT(people) AS people_count
FROM table
WHERE type = 1
GROUP BY date, campaign_name
HAVING people_count < 100
) AS filter
ON
full_data.date = filter.date
AND full_data.campaign_name = filter.campaign_name
WHERE
filter.date IS NULL
AND filter.campaign_name IS NULL
The first subselect is basically your current query without any attempt at using HAVING to filter out results. The second subselect is used to find all date/campaign name combos which have people_count > 100 and use those as a filter for against the full data set.
I'm getting grey hair by now...
I have a table like this.
ID - Place - Person
1 - London - Anna
2 - Stockholm - Johan
3 - Gothenburg - Anna
4 - London - Nils
And I want to get the result where all the different persons are included, but I want to choose which Place to order by.
For example. I want to get a list where they are ordered by LONDON and the rest will follow, but distinct on PERSON.
Output like this:
ID - Place - Person
1 - London - Anna
4 - London - Nils
2 - Stockholm - Johan
Tried this:
SELECT ID, Person
FROM users
ORDER BY FIELD(Place,'London'), Person ASC "
But it gives me:
ID - Place - Person
1 - London - Anna
4 - London - Nils
3 - Gothenburg - Anna
2 - Stockholm - Johan
And I really dont want Anna, or any person, to be in the result more then once.
This is one way to get the specified output, but this uses MySQL specific behavior which is not guaranteed:
SELECT q.ID
, q.Place
, q.Person
FROM ( SELECT IF(p.Person<=>#prev_person,0,1) AS r
, #prev_person := p.Person AS person
, p.Place
, p.ID
FROM users p
CROSS
JOIN (SELECT #prev_person := NULL) i
ORDER BY p.Person, !(p.Place<=>'London'), p.ID
) q
WHERE q.r = 1
ORDER BY !(q.Place<=>'London'), q.Person
This query uses an inline view to return all the rows in a particular order, by Person, so that all of the 'Anna' rows are together, followed by all the 'Johan' rows, etc. The set of rows for each person is ordered by, Place='London' first, then by ID.
The "trick" is to use a MySQL user variable to compare the values from the current row with values from the previous row. In this example, we're checking if the 'Person' on the current row is the same as the 'Person' on the previous row. Based on that check, we return a 1 if this is the "first" row we're processing for a a person, otherwise we return a 0.
The outermost query processes the rows from the inline view, and excludes all but the "first" row for each Person (the 0 or 1 we returned from the inline view.)
(This isn't the only way to get the resultset. But this is one way of emulating analytic functions which are available in other RDBMS.)
For comparison, in databases other than MySQL, we could use SQL something like this:
SELECT ROW_NUMBER() OVER (PARTITION BY t.Person ORDER BY
CASE WHEN t.Place='London' THEN 0 ELSE 1 END, t.ID) AS rn
, t.ID
, t.Place
, t.Person
FROM users t
WHERE rn=1
ORDER BY CASE WHEN t.Place='London' THEN 0 ELSE 1 END, t.Person
Followup
At the beginning of the answer, I referred to MySQL behavior that was not guaranteed. I was referring to the usage of MySQL User-Defined variables within a SQL statement.
Excerpts from MySQL 5.5 Reference Manual http://dev.mysql.com/doc/refman/5.5/en/user-variables.html
"As a general rule, other than in SET statements, you should never assign a value to a user variable and read the value within the same statement."
"For other statements, such as SELECT, you might get the results you expect, but this is not guaranteed."
"the order of evaluation for expressions involving user variables is undefined."
Try this:
SELECT ID, Place, Person
FROM users
GROUP BY Person
ORDER BY FIELD(Place,'London') DESC, Person ASC;
You want to use group by instead of distinct:
SELECT ID, Person
FROM users
GROUP BY ID, Person
ORDER BY MAX(FIELD(Place, 'London')), Person ASC;
The GROUP BY does the same thing as SELECT DISTINCT. But, you are allowed to mention other fields in clauses such as HAVING and ORDER BY.
I think it will be easiest to start with the table I have and the result I am aiming for.
Name | Date
A | 03/01/2012
A | 03/01/2012
B | 02/01/2012
A | 02/01/2012
B | 02/01/2012
A | 02/01/2012
B | 01/01/2012
B | 01/01/2012
A | 01/01/2012
I want the result of my query to be:
Name | 01/01/2012 | 02/01/2012 | 03/01/2012
A | 1 | 2 | 2
B | 2 | 2 | 0
So basically I want to count the number of rows that have the same date, but for each individual name. So a simple group by of dates won't do because it would merge the names together. And then I want to output a table that shows the counts for each individual date using php.
I've seen answers suggest something like this:
SELECT
NAME,
SUM(CASE WHEN GRADE = 1 THEN 1 ELSE 0 END) AS GRADE1,
SUM(CASE WHEN GRADE = 2 THEN 1 ELSE 0 END) AS GRADE2,
SUM(CASE WHEN GRADE = 3 THEN 1 ELSE 0 END) AS GRADE3
FROM Rodzaj
GROUP BY NAME
so I imagine there would be a way for me to tweak that but I was wondering if there is another way, or is that the most efficient?
I was perhaps thinking if the while loop were to output just one specific name and date each time along with the count, so the first result would be A,01/01/2012,1 then the next A,02/01/2012,2 - A,03/01/2012,3 - B,01/01/2012,2 etc. then perhaps that would be doable through a different technique but not sure if something like that is possible and if it would be efficient.
So I'm basically looking to see if anyone has any ideas that are a bit outside the box for this and how they would compare.
I hope I explained everything well enough and thanks in advance for any help.
You have to include two columns in your GROUP BY:
SELECT name, COUNT(*) AS count
FROM your_table
GROUP BY name, date
This will get the counts of each name -> date combination in row-format. Since you also wanted to include a 0 count if the name didn't have any rows on a certain date, you can use:
SELECT a.name,
b.date,
COUNT(c.name) AS date_count
FROM (SELECT DISTINCT name FROM your_table) a
CROSS JOIN (SELECT DISTINCT date FROM your_table) b
LEFT JOIN your_table c ON a.name = c.name AND
b.date = c.date
GROUP BY a.name,
b.date
SQLFiddle Demo
You're asking for a "pivot". Basically, it is what it is. The real problem with a pivot is that the column names must adapt to the data, which is impossible to do with SQL alone.
Here's how you do it:
SELECT
Name,
SUM(`Date` = '01/01/2012') AS `01/01/2012`,
SUM(`Date` = '02/01/2012') AS `02/01/2012`,
SUM(`Date` = '03/01/2012') AS `03/01/2012`
FROM mytable
GROUP BY Name
Note the cool way you can SUM() a condition in mysql, becasue in mysql true is 1 and false is 0, so summing a condition is equivalent to counting the number of times it's true.
It is not more efficient to use an inner group by first.
Just in case anyone is interested in what was the best method:
Zane's second suggestion was the slowest, I loaded in a third of the data I did for the other two and it took quite a while. Perhaps on smaller tables it would be more efficient, and although I am not working with a huge table roughly 28,000 rows was enough to create significant lag, with the between clause dropping the result to about 4000 rows.
Bohemian's answer gave me the least amount to code, I threw in a loop to create all the case statements and it worked with relative ease. The benefit of this method was the simplicity, besides creating the loop for the cases, the results come in without the need for any php tricks, just simple foreach to get all the columns. Recommended for those not confident with php.
However, I found Zane's first suggestion the quickest performing and despite the need for extra php coding it seems I will be sticking with this method. The disadvantage of this method is that it only gives the dates that actually have data, so creating a table with all the dates becomes a bit more complicated. What I did was create a variable that keeps track of what date it is supposed to be compared to the table column which is reset on each table row, when the result of the query is equal to that date it echoes the value otherwise it does a while loop echoing table cells with 0 until the dates do match. It also had to do a check to see if the 'Name' value is still the same and if not it would switch to the next row after filling in any missing cells with 0 to the end of that row. If anyone is interested in seeing the code you can message me.
Results of the two methods over 3 months of data (a column for each day so roughly 90 case statements) ~ 12,000 rows out of 28,000:Bohemian's Pivot - ~0.158s (highest seen ~0.36s)Zane's Double Group by - ~0.086s (highest seen ~0.15s)
The actual question is a little more complex than that, so here goes.
I have a website which reviews games. Ratings/reviews are posted for each game, and so I have a MySQL database to handle it all.
Thing is, I'd really like a page that showed what score (out of 10) meant what, and to illustrate it would have the game that was last reviewed as an example. I can always do it without, but this would be cooler.
So the query should return something like this (but running from 10 to 0):
|---------------*----------------*-----------------*-----------------|
* game.gameName | game.gameImage | review.ourScore | review.postedOn *
|---------------*----------------*-----------------*-----------------|
| Top Game | img | 10 | (unix timestamp)|
| NearlyTop Game| img | 9 | (unix timestamp)|
| Great Game | img | 8 | (unix timestamp)|
|---------------*----------------*-----------------*-----------------|
The information is in two tables, game and review. I think you'd use MAX() to find out the last timestamp and corresponding game information, but as far as complex queries go, I'm in way over my head.
Of course this could be done with 10 simple SELECTs but I'm sure there must be a way to do this in one query.
Thanks for any help.
Here is an ugly solution I found:
This query simply gets the IDs and scores of the reviews that you want to look at. I have included it so that you can understand what the trick is, without getting distracted by other stuff:
SELECT * FROM
(SELECT reviewID, ourScore FROM review ORDER BY postedOn DESC) as `r`
GROUP BY ourScore
ORDER BY ourScore DESC;
This exploits MySQL's 'GROUP BY' behavior. When the grouping is done, if the source rows have different values for different columns, then the value of the topmost source row is used. So if you had rows in this order:
reviewId Score
1 3
0 3
2 3
Then after you group by score, the reviewId is 1 because that row was on the top:
reviewId Score
1 3
So we want to put the most recent review on the top before we do the group by. Since ORDERing is always dones after grouping, in a single SELECT statement, I had to make a subquery to accomplish this. Now we just dress up this query a little bit to get all the fields you wanted:
SELECT `r`.*, game.gameName, game.gameImage FROM
(SELECT reviewID, ourScore, postedOn, gameID FROM review ORDER BY **postedOn DESC**) as `r`
JOIN game ON `r`.gameID = game.gameID
GROUP BY ourScore
ORDER BY ourScore DESC;
That should work.
SELECT DISTINCT game.gameName, game.gameImage, review.ourScore FROM game
LEFT JOIN review
ON game.ID = review.gameID
ORDER BY review.postedOn
LIMIT 10
Or something like that, check out how to use the Distinct first, I'm not sure on the syntax, and you may have to tell the ORDER BY DESC or ASC depending on what you want.
Well..
SELECT game.gameName, game.gameImage, review.ourScore
FROM game
LEFT JOIN review ON game.gameID = review.gameID
GROUP BY review.ourScore DESC
LIMIT 10
returns a list of games grouped by each individual score. But this isn't what I want, I want the game that is last posted - this is why the timestamp is important. With that query, MySQL returns the first result it can find.
I think this would work:
select g.gameName, g.gameImage, r.ourScore, r.postedOn
from game g, review r
where g.gameId = r.gameId
and r.postedOn = (select max(sr.postedOn)
from review sr where sr.ourScore = r.ourScore)
group by r.ourScore
order by r.ourScore desc;
Edit: above SQL was corrected after David Grayson's comment. I think this query is pretty easy to understand but probably performs poorly compared with his solution.