i tried using this query:
"SELECT * FROM guests WHERE event_id=".$id." GROUP BY member_id;"
and I'm getting this error:
ERROR: column "guests.id" must appear in the GROUP BY clause or be used in an aggregate function
can anyone explain how i can work around this?
You can't Group By without letting the Select know what to take, and how to group.
Try
SELECT guests.member_id FROM guests WHERE event_id=".$id." GROUP BY member_id;
IF you need to get more info from this table about the guests, you'll need to add it to the Group By.
Plus, it seems like your select should actually be
SELECT guests.id FROM guests WHERE event_id=".$id." GROUP BY id;
Each of the columns used in a group by query needs to be specifically called out (ie, don't do SELECT * FROM ...), as you need to use them in some sort of aggregate function (min/max/sum/avg/count/etc) or be part of the group by clause.
For example:
SELECT instrument, detector, min(date_obs), max(date_obs)
FROM observations
WHERE observatory='SOHO'
GROUP BY instrument, detector;
Related
From my understanding queries that rely on one or more aggregate functions as well as at least one single row function require the single row functions to be placed
in a group by clause, which makes sense overall.
However I'm working through problems in an online resource and ran into the question in the picture, my logic behind why I answered it executes successfully but gives improper output is that the subquery is a query that has only an aggregate function, leaving me to believe that it requires no group by, why is it that this requires a group by in the subquery?
Already cleared by Gordon, "Nested aggregate requires a GROUP BY clause". If we consider the query into 2 parts, first part works fine if Having is given with specific value.
Example:
Run Queries in this link:
https://livesql.oracle.com/apex/f?p=590:1:104596775146183::NO:RP::
select count(*), PROD_CATEGORY_ID from SH.PRODUCTS group by PROD_CATEGORY_ID
having count(*)>15;
But we get error if we combine 2 aggregate functions,
select max(count(PROD_CATEGORY_ID)) from SH.PRODUCTS ; --> Throws ORA-00978
select max(count(PROD_CATEGORY_ID)) from SH.PRODUCTS
group by PROD_CATEGORY_ID; -->Gives max count of prod_cat
Gives final result:
select count(*), PROD_CATEGORY_ID from SH.PRODUCTS
group by PROD_CATEGORY_ID
having count(*)=(select max(count(*)) from SH.PRODUCTS group by PROD_CATEGORY_ID);
Good Examples in link:
https://mahtodeepak05.wordpress.com/2014/12/17/aggregate-function-nesting-in-oracle/
You can easily test this:
select max(count(*))
from dual;
The error is:
ORA-00978: nested group function without GROUP BY
So, a nested group by seems to require a GROUP BY.
I am trying to use group by with count function but this doesn't work.
SELECT
projects.AgencyId,
projects.ProgramId,
count(projects.ProjStatusByMin) as status,
projects.ProjStatusByMin
from
projects
where
projects.AgencyId=40
group by
projects.ProjStatusByMin
This above code works in MySQL perfectly now i want to achieve the same thing in SQL Server.
Select
ProjStatusByMin,
COUNT(ProjStatusByMin) [projstatus]
from
Projects
where
AgencyId=40
group by
ProjStatusByMin,AgencyId,ProjId
However if i select a single column like the bellow code then group by work
Select
ProjStatusByMin,
COUNT(ProjStatusByMin) [projstatus]
from
Projects
where
AgencyId=40
group by
ProjStatusByMin
Now how can I achieve group by with multi column selected?
You have to add all the columns (except for the one in the count function) to the group by clause.
SELECT projects.AgencyId,projects.ProgramId,count(projects.ProjStatusByMin) as status,
projects.ProjStatusByMin
from projects
where projects.AgencyId=40
group by projects.ProjStatusByMin, projects.AgencyId,projects.ProgramId
In Sql Server you have to write all the column names in group by clause which you are going to select in the select statement.
I ran a query against Northwind database Products Table like below
select * from Northwind.dbo.Products GROUP BY CategoryID and i was hit with a error. I am sure you will also be hit by same error. So what is the correct statement that i need to execute to group all products with respect to their category id's.
edit: this like really helped understand a lot
http://weblogs.sqlteam.com/jeffs/archive/2007/07/20/but-why-must-that-column-be-contained-in-an-aggregate.aspx
You need to use an Aggregate function and then group by any non-aggregated columns.
I recommend reading up on GROUP BY.
If you're using GROUP BY in a query, all items in your SELECT statement must either be contained as part of an aggregate function, e.g. Sum() or Count(), else they will also need to be included in the GROUP BY clause.
Because you are using SELECT *, this is equivalent to listing ALL columns in your SELECT.
Therefore, either list them all in the GROUP BY too, use aggregating functions for the rest where possible, or only select the CategoryID.
I have a table with 3 columns:
userid mac_address count
The entries for one user could look like this:
57193 001122334455 42
57193 000C6ED211E6 15
57193 FFFFFFFFFFFF 2
I want to create a view that displays only those MAC's that are considered "commonly used" for this user. For example, I want to filter out the MAC's that are used <10% compared to the most used MAC-address for that user. Furthermore I want 1 row per user. This could easily be achieved with a GROUP BY, HAVING & GROUP_CONCAT:
SELECT userid, GROUP_CONCAT(mac_address SEPARATOR ',') AS macs, count
FROM mactable
GROUP BY userid
HAVING count*10 >= MAX(count)
And indeed, the result is as follows:
57193 001122334455,000C6ED211E6 42
However I really don't want the count-column in my view. But if I take it out of the SELECT statement, I get the following error:
#1054 - Unknown column 'count' in 'having clause'
Is there any way I can perform this operation without being forced to have a nasty count-column in my view? I know I can probably do it using inner queries, but I would like to avoid doing that for performance reasons.
Your help is very much appreciated!
As HAVING explicitly refers to the column names in the select list, it is not possible what you want.
However, you can use your select as a subselect to a select that returns only the rows you want to have.
SELECT a.userid, a.macs
FROM
(
SELECT userid, GROUP_CONCAT(mac_address SEPARATOR ',') AS macs, count
FROM mactable
GROUP BY userid
HAVING count*10 >= MAX(count)
) as a
UPDATE:
Because of a limitation of MySQL this is not possible, although it works in other DBMS like Oracle.
One solution would be to create a view for the subquery. Another solution seems cleaner:
CREATE VIEW YOUR_VIEW (userid, macs) AS
SELECT userid, GROUP_CONCAT(mac_address SEPARATOR ',') AS macs, count
FROM mactable
GROUP BY userid
HAVING count*10 >= MAX(count)
This will declare the view as returning only the columns userid and macs although the underlying SELECT statement returns more columns than those two.
Although I am not sure, whether the non-DBMS MySQL supports this or not...
Given a command in SQL;
SELECT ...
FROM ...
GROUP BY ...
Can I group by something that isn't in the SELECT line?
Yes.
This is often used in the superaggregate queries like this:
SELECT AVG(cnt)
FROM (
SELECT COUNT(*) AS cnt
FROM sales
GROUP BY
product
HAVING COUNT(*) > 10
) q
, which aggregate the aggregates.
Yes of course e.g.
select
count(*)
from
some_table_with_updated_column
group by
trunc(updated, 'MM.YYYY')
Yes you can do it, but if you do that you won't be able to tell which result is for which group.
As a result, you almost always want to return the columns you've grouped by in the select clause. But you don't have to.
Yes, you can. Example:
select count(1)
from sales
group by salesman_id
What you can't do, of course, if having something on your select clause (other than aggregate functions) that are not part of the group by clause.
Hmm, I think the question should have been in the other way round like,
Can I SELECT something that is not there in the GROUP BY?
It's alright to write a code like:
SELECT customerId, count(orderId) FROM orders
GROUP BY customerId, orderedOn
If you want to find out the number of orders done by a customer datewise.
But you cannot do it the other way round:
SELECT customerId, orderedOn count(orderId) FROM orders
GROUP BY customerId
You can issue an aggregate function on the column that is not there in the group by. But you cannot give it in the select line without the aggregate function. As it will not make much sense. Like for the above query. You group by just customerId for order counts and you want the date also to be printed in the output??!! You don't involve the date factor in the group for counting then will it mean something to have a date in it?
I don't know about other DBMS' but DB2/z, for one, does this just fine. It's not required to have the column in the select portion but, of course, it does have to extract the data from the table in order to aggregate so you're probably not saving any time by leaving it off. You should only select the columns that you need, aggregation of the data is a separate task from that.
I'm pretty certain the SQL standard allows this (although that's only based on the knowledge that the mainframe DB2 product follows it pretty closely).