I'll be upfront, this is a homework question, but I've been stuck on this one for hours and I just was looking for a push in the right direction. First I'll give you the relations and the hw question for background, then I'll explain my question:
Branch (BookCode, BranchNum, OnHand)
HW problem: List the BranchNum for all branches that have at least one book that has at least 10 copies on hand.
My question: I understand that I must take the SUM(OnHand) grouped by BookCode, but how do I then take that and group it by BranchNum? This is logically what I come up with and various versions:
select distinct BranchNum
from Inventory
where sum(OnHand) >= 10
group by BookCode;
but I keep getting an error that says "Invalid use of group function."
Could someone please explain what is wrong here?
UPDATE:
I understand now, I had to use the HAVING statement, the basic form is this:
select distinct (what you want to display)
from (table)
group by
having
Try this one.
SELECT BranchNum
FROM Inventory
GROUP BY BranchNum
HAVING SUM(OnHand) >= 10
You can also find Group By Clause with example here.
Although all comments in the question seem to be valid and add information they all seem to be missing why your query is not working. The reason is simple and is strictly related by the state/phase at which the sum is calculated.
The where clause is the first thing that will get executed. This means it will filter all rows at the beginning. Then the group by will come in effect and will merge all rows that are not specified in the clause and apply the aggregated functions (if any).
So if you try to add an aggregated function to the where clause you're trying to aggregate before data is being grouped by and even filtered. The having clause gets executed after the group by and allows you to filter the aggregated functions, as they have already been calculated.
That's why you can write HAVING SUM(OnHand) >= 10 and you can't write WHERE SUM(OnHand) >= 10.
Hope this helps!
Related
I want to group by two columns, however MS Access won't let me do it.
Here is the code I wrote:
SELECT
tbl_Produktion.Datum, tbl_Produktion.Schichtleiter,
tbl_Produktion.ProduktionsID, tbl_Produktion.Linie,
tbl_Produktion.Schicht, tbl_Produktion.Anzahl_Schichten_P,
tbl_Produktion.Schichtteam, tbl_Produktion.Von, tbl_Produktion.Bis,
tbl_Produktion.Pause, tbl_Produktion.Kunde, tbl_Produktion.TeileNr,
tbl_Produktion.FormNr, tbl_Produktion.LabyNr,
SUM(tbl_Produktion.Stueckzahl_Prod),
tbl_Produktion.Stueckzahl_Ausschuss, tbl_Produktion.Ausschussgrund,
tbl_Produktion.Kommentar, tbl_Produktion.StvSchichtleiter,
tbl_Produktion.Von2, tbl_Produktion.Bis2, tbl_Produktion.Pause2,
tbl_Produktion.Arbeiter3, tbl_Produktion.Von3, tbl_Produktion.Bis3,
tbl_Produktion.Pause3, tbl_Produktion.Arbeiter4,
tbl_Produktion.Von4, tbl_Produktion.Bis4, tbl_Produktion.Pause4,
tbl_Produktion.Leiharbeiter5, tbl_Produktion.Von5,
tbl_Produktion.Bis5, tbl_Produktion.Pause5,
tbl_Produktion.Leiharbeiter6, tbl_Produktion.Von6,
tbl_Produktion.Bis6, tbl_Produktion.Pause6, tbl_Produktion.Muster
FROM
tbl_Personal
INNER JOIN
tbl_Produktion ON tbl_Personal.PersID = tbl_Produktion.Schichtleiter
GROUP BY
tbl_Produktion.Datum, tbl_Produktion.Schichtleiter;
It works when I group it by all the columns, but not like this.
The error message say that the rest of the columns aren't part of the aggregation-function (translated from german to english as best as I could).
PS.: I also need the sum of "tbl_Produktion.Stueckzahl_Prod" therefore I tried using the SUM function (couldn't try it yet).
Have you tried something along these lines?
SELECT
tbl_Produktion.Datum, tbl_Produktion.Schichtleiter,
MAX(tbl_Produktion.ProduktionsID), MAX(tbl_Produktion.Linie),
MAX(tbl_Produktion.Schicht), MAX(tbl_Produktion.Anzahl_Schichten_P),
MAX(tbl_Produktion.Schichtteam), MAX(tbl_Produktion.Von), MAX(tbl_Produktion.Bis),
SUM(tbl_Produktion.Stueckzahl_Prod)
FROM
tbl_Personal
INNER JOIN
tbl_Produktion ON tbl_Personal.PersID = tbl_Produktion.Schichtleiter
GROUP BY
tbl_Produktion.Datum, tbl_Produktion.Schichtleiter;
I have used the MAX function for all the data except the two items you specify in the GROUP BY and the one where you desire the SUM. I took the liberty of leaving out mush of your data just to get started.
Using the MAX function turns out to be a convenient workaround when the data item is known to be unique within each group. We cannot know your data or your itent, so we cannot tell you whether MAX will yield the results you need.
If you use an aggregation function in the select clause, you must group by every column that you're selecting that's not an aggregation. If you don't want to do that for some reason (perhaps it changes the output of the aggregation in way that you don't intend) you either must think of an aggregate to use (pick a value. Average? Max? Min?) or just do two selects, one for the aggregate, and one for the non-aggregates. But, then, you have to decide how to get the non-aggregated fields that make sense for the aggregate (or show them all in a table, I suppose?)
I'm stuck in an (apparently) extremely trivial task that I can't make work , and I really feel no chance than to ask for advice.
I used to deal with PHP/MySQL more than 10 years ago and I might be quite rusty now that I'm dealing with an SQLite DB using Qt5.
Basically I'm selecting some records while wanting to make some math operations on the fetched columns. I recall (and re-read some documentation and examples) that the keyword "AS" is going to conveniently rename (alias) a value.
So for example I have this query, where "X" is an integer number that I render into this big Qt string before executing it with a QSqlQuery. This query lets me select all the electronic components used in a Project and calculate how many of them to order (rounding to the nearest multiple of 5) and the total price per component.
SELECT Inventory.id, UsedItems.pid, UsedItems.RefDes, Inventory.name, Inventory.category,
Inventory.type, Inventory.package, Inventory.value, Inventory.manufacturer,
Inventory.price, UsedItems.qty_used as used_qty,
UsedItems.qty_used*X AS To_Order,
ROUND((UsedItems.qty_used*X/5)+0.5)*5*CAST((X > 0) AS INT) AS Nearest5,
Inventory.price*Nearest5 AS TotPrice
FROM Inventory
LEFT JOIN UsedItems ON Inventory.id=UsedItems.cid
WHERE UsedItems.pid='1'
ORDER BY RefDes, value ASC
So, for example, I aliased UsedItems.qty_used as used_qty. At first I tried to use it in the next field, multiplying it by X, writing "used_qty*X AS To_Order" ... Query failed. Well, no worries, I had just put the original tab.field name and it worked.
Going further, I have a complex calculation and I want to use its result on the next field, but the same issue popped out: if I alias "ROUND(...)" AS Nearest5, and then try to use this value by multiplying it in the next field, the query will fail.
Please note: the query WORKS, but ONLY if I don't use aliases in the following fields, namely if I don't use the alias Nearest5 in the TotPrice field. I just want to avoid re-writing the whole ROUND(...) thing for the TotPrice field.
What am I missing/doing wrong? Either SQLite does not support aliases on the same query or I am using a wrong syntax and I am just too stuck/confused to see the mistake (which I'm sure it has to be really stupid).
Column aliases defined in a SELECT cannot be used:
For other expressions in the same SELECT.
For filtering in the WHERE.
For conditions in the FROM clause.
Many databases also restrict their use in GROUP BY and HAVING.
All databases support them in ORDER BY.
This is how SQL works. The issue is two things:
The logic order of processing clauses in the query (i.e. how they are compiled). This affects the scoping of parameters.
The order of processing expressions in the SELECT. This is indeterminate. There is no requirement for the ordering of parameters.
For a simple example, what should x refer to in this example?
select x as a, y as x
from t
where x = 2;
By not allowing duplicates, SQL engines do not have to make a choice. The value is always t.x.
You can try with nested queries.
A SELECT query can be nested in another SELECT query within the FROM clause;
multiple queries can be nested, for example by following the following pattern:
SELECT *,[your last Expression] AS LastExp From (SELECT *,[your Middle Expression] AS MidExp FROM (SELECT *,[your first Expression] AS FirstExp FROM yourTables));
Obviously, respecting the order that the expressions of the innermost select query can be used by subsequent select queries:
the first expressions can be used by all other queries, but the other intermediate expressions can only be used by queries that are further upstream.
For your case, your query may be:
SELECT *, PRC*Nearest5 AS TotPrice FROM (SELECT *, ROUND((UsedItems.qty_used*X/5)+0.5)*5*CAST((X > 0) AS INT) AS Nearest5 FROM (SELECT Inventory.id, UsedItems.pid, UsedItems.RefDes, Inventory.name, Inventory.category, Inventory.type, Inventory.package, Inventory.value, Inventory.manufacturer, Inventory.price AS PRC, UsedItems.qty_used*X AS To_Order FROM Inventory LEFT JOIN UsedItems ON Inventory.id=UsedItems.cid WHERE UsedItems.pid='1' ORDER BY RefDes, value ASC))
I'm having trouble with Microsoft Access 2003, it's complaining about this statement:
select cardnr
from change
where year(date)<2009
group by cardnr
having max(time+date) = (time+date) and cardto='VIP'
What I want to do is, for every distinct cardnr in the table change, to find the row with the latest (time+date) that is before year 2009, and then just select the rows with cardto='VIP'.
This validator says it's OK, Access says it's not OK.
This is the message I get: "you tried to execute a query that does not include the specified expression 'max(time+date)=time+date and cardto='VIP' and cardnr=' as part of an aggregate function."
Could someone please explain what I'm doing wrong and the right way to do it? Thanks
Note: The field and table names are translated and do not collide with any reserved words, I have no trouble with the names.
Try to think of it like this - HAVING is applied after the aggregation is done.
Therefore it can not compare to unaggregated expressions (neither for time+date, nor for cardto).
However, to get the last (principle is the same for getting rows related to other aggregated functions as weel) time and date you can do something like:
SELECT cardnr
FROM change main
WHERE time+date IN (SELECT MAX(time+date)
FROM change sub
WHERE sub.cardnr = main.cardnr AND
year(date)<2009
AND cardto='VIP')
(assuming that date part on your time field is the same for all the records; having two fields for date/time is not in your best interest and also using reserved words for field names can backfire in certain cases)
It works because the subquery is filtered only on the records that you are interested in from the outer query.
Applying the same year(date)<200 and cardto='VIP' to the outer query can improve performance further.
So I got this statement, which works fine:
SELECT MAX(patient_history_date_bio) AS med_date, medication_name
FROM biological
WHERE patient_id = 12)
GROUP BY medication_name
But, I would like to have the corresponding medication_dose also. So I type this up
SELECT MAX(patient_history_date_bio) AS med_date, medication_name, medication_dose
FROM biological
WHERE (patient_id = 12)
GROUP BY medication_name
But, it gives me an error saying:
"coumn 'biological.medication_dose' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.".
So I try adding medication_dose to the GROUP BY clause, but then it gives me extra rows that I don't want.
I would like to get the latest row for each medication in my table. (The latest row is determined by the max function, getting the latest date).
How do I fix this problem?
Use:
SELECT b.medication_name,
b.patient_history_date_bio AS med_date,
b.medication_dose
FROM BIOLOGICAL b
JOIN (SELECT y.medication_name,
MAX(y.patient_history_date_bio) AS max_date
FROM BIOLOGICAL y
GROUP BY y.medication_name) x ON x.medication_name = b.medication_name
AND x.max_date = b.patient_history_date_bio
WHERE b.patient_id = ?
If you really have to, as one quick workaround, you can apply an aggregate function to your medication_dose such as MAX(medication_dose).
However note that this is normally an indication that you are either building the query incorrectly, or that you need to refactor/normalize your database schema. In your case, it looks like you are tackling the query incorrectly. The correct approach should the one suggested by OMG Poinies in another answer.
You may be interested in checking out the following interesting article which describes the reasons behind this error:
But WHY Must That Column Be Contained in an Aggregate Function or the GROUP BY clause?
You need to put max(medication_dose) in your select. Group by returns a result set that contains distinct values for fields in your group by clause, so apparently you have multiple records that have the same medication_name, but different doses, so you are getting two results.
By putting in max(medication_dose) it will return the maximum dose value for each medication_name. You can use any aggregate function on dose (max, min, avg, sum, etc.)
Hey guys. This is a follow-on from this question:
After getting the right data and making some tweaks based on requests from business, I've now got this mini-beast on my hands. This query should return the total number of new jobseeker registrations and the number of new uploaded CV's:
SELECT COUNT(j.jobseeker_id) as new_registrations,
(
SELECT
COUNT(c.cv_id)
FROM
tb_cv as c, tb_jobseeker, tb_industry
WHERE
UNIX_TIMESTAMP(c.created_at) >= '1241125200'
AND
UNIX_TIMESTAMP(c.created_at) <= '1243717200'
AND
tb_jobseeker.industry_id = tb_industry.industry_id
)
AS uploaded_cvs
FROM
tb_jobseeker as j, tb_industry as i
WHERE
j.created_at BETWEEN '2009-05-01' AND '2009-05-31'
AND
i.industry_id = j.industry_id
GROUP BY i.description, MONTH(j.created_at)
Notes:
- The two values in the UNIX TIMESTAMP functions are passed in as parameters from the report module in our backend.
Every time I run it, MySQL chokes and lingers silently into the ether of the Interweb.
Help is appreciated.
Update: Hey guys. Thanks a lot for all the thoughtful and helpful comments. I'm only 2 weeks into my role here, so I'm still learning the schema. So, this query is somewhere between a thumbsuck and an educated guess. Will start to answer all your questions now.
tb_cv is not connected to the other tables in the sub-query. I guess this is the root cause for the slow query. It causes generation of a Cartesian product, yielding a lot more rows than you probably need.
Other than that I'd say you need indexes on tb_jobseeker.created_at, tb_cv.created_at and tb_industry.industry_id, and you might want to get rid of the UNIX_TIMESTAMP() calls in the sub-query since they prevent use of an index. Use BETWEEN and the actual field values instead.
Here is my attempt at understanding your query and writing a better version. I guess you want to get the count of new jobseeker registrations and new uploaded CVs per month per industry:
SELECT
i.industry_id,
i.description,
MONTH(j.created_at) AS month_created,
YEAR(j.created_at) AS year_created,
COUNT(DISTINCT j.jobseeker_id) AS new_registrations,
COUNT(cv.cv_id) AS uploaded_cvs
FROM
tb_cv AS cv
INNER JOIN tb_jobseeker AS j ON j.jobseeker_id = cv.jobseeker_id
INNER JOIN tb_industry AS i ON i.industry_id = j.industry_id
WHERE
j.created_at BETWEEN '2009-05-01' AND '2009-05-31'
AND cv.created_at BETWEEN '2009-05-01' AND '2009-05-31'
GROUP BY
i.industry_id,
i.description,
MONTH(j.created_at),
YEAR(j.created_at)
A few things I noticed while writing the query:
you GROUP BY values you don't output in the end. Why? (I've added the grouped field to the output list.)
you JOIN three tables in the sub-query while only ever using values from one of them. Why? I don't see what it would be good for, other than filtering out CV records that don't have a jobseeker or an industry attached — which I find hard to imagine. (I've removed the entire sub-query and used a simple COUNT instead.)
Your sub-query returns the same value every time. Did you maybe mean to correlate it in some way, to the industry maybe?.
The sub-query runs once for every record in a grouped query without being wrapped in an aggregate function.
First and foremost it may be worth moving the 'UNIX_TIMESTAMP' conversions to the other side of the equation (that is, perform a reverse function on the literal timestamp values at the other side of the >= and <=). That'll avoid the inner query having to perform the conversions for every record, rather than once for the query.
Also, why does the uploaded_cvs query not have any where clause linking it to the outer query? Am I missing something here?