Sample example:
SELECT
Equip.name, equip.type, region.regionname, region.equipfk
FROM
Equip
INNER JOIN
region on Equip.equippk = region.equipfk
GROUP BY
Equip.Name, region.equipfk
Expected output :
name type regionname equipfk
----------------------------------------
TCT Steel detroit 8235
TCT steel detroit 8235
GTH COPPER michigan 8569
GCT COPPER michigan 8569
I have a table containing 10 columns. I want to group each row by some ids using group by clause. I dont want to use any of the aggregate functions in select query. Is there is any alternate way to use group by clause and avoid aggregate functions in the select query..
Thanks in advance.
It sounds like you're using GROUP BY in an attempt to sort the rows (which it only does by a coincidental side effect that isn't guaranteed). If that's the case, you need ORDER BY instead:
SELECT
Equip.name, equip.type, region.regionname, region.equipfk
FROM
Equip
INNER JOIN
region on Equip.equippk = region.equipfk
ORDER BY
Equip.Name, region.equipfk
Both GROUP BY and DISTINCT may produce output that appears to be sorted - but this is only a side effect of how they've been implemented, and many things (load on the server, server configuration, hot fixes, service packs, major upgrades) may change the order in which rows are returned - unless you also have an ORDER BY clause.
Related
So I have complicated query, to simplify let it be like
SELECT
t.*,
SUM(a.hours) AS spent_hours
FROM (
SELECT
person.id,
person.name,
person.age,
SUM(contacts.id) AS contact_count
FROM
person
JOIN contacts ON contacts.person_id = person.id
) AS t
JOIN activities AS a ON a.person_id = t.id
GROUP BY t.id
Such query works fine in MySQL, but Postgres needs to know that GROUP BY field is unique, and despite it actually is, in this case I need to GROUP BY all returned fields from returned t table.
I can do that, but I don't believe that will work efficiently with big data.
I can't JOIN with activities directly in first query, as person can have several contacts which will lead query counting hours of activity several time for every joined contact.
Is there a Postgres way to make this query work? Maybe force to treat Postgres t.id as unique or some other solution that will make same in Postgres way?
This query will not work on both database system, there is an aggregate function in the inner query but you are not grouping it(unless you use window functions). Of course there is a special case for MySQL, you can use it with disabling "sql_mode=only_full_group_by". So, MySQL allows this usage because of it' s database engine parameter, but you cannot do that in PostgreSQL.
I knew MySQL allowed indeterminate grouping, but I honestly never knew how it implemented it... it always seemed imprecise to me, conceptually.
So depending on what that means (I'm too lazy to look it up), you might need one of two possible solutions, or maybe a third.
If you intent is to see all rows (perform the aggregate function but not consolidate/group rows), then you want a windowing function, invoked by partition by. Here is a really dumbed down version in your query:
.
SELECT
t.*,
SUM (a.hours) over (partition by t.id) AS spent_hours
FROM t
JOIN activities AS a ON a.person_id = t.id
This means you want all records in table t, not one record per t.id. But each row will also contain a sum of the hours for all values that value of id.
For example the sum column would look like this:
Name Hours Sum Hours
----- ----- ---------
Smith 20 120
Jones 30 30
Smith 100 120
Whereas a group by would have had Smith once and could not have displayed the hours column in detail.
If you really did only want one row per t.id, then Postgres will require you to tell it how to determine which row. In the example above for Smith, do you want to see the 20 or the 100?
There is another possibility, but I think I'll let you reply first. My gut tells me option 1 is what you're after and you want the analytic function.
I need to show all clients entered into the system for a date range.
All clients are assigned to a group, but not necessarily to a staff.
When I run the query as such:
SELECT
clients.name_lastfirst_cs,
to_char (clients.date_intake,'MM/DD/YY')AS Date_Created,
clients.client_id,
clients.display_intake,
staff.staff_name_cs,
groups.name
FROM
public.clients,
public.groups,
public.staff,
public.link_group
WHERE
clients.zrud_staff = staff.zzud_staff AND
clients.zzud_client = link_group.zrud_client AND
groups.zzud_group = link_group.zrud_group AND
clients.date_intake BETWEEN (now() - '8 days'::interval)::timestamp AND now()
ORDER BY
groups.name ASC,
clients.client_id ASC,
staff.staff_name_cs ASC
I get 121 entries
if I comment out:
SELECT
clients.name_lastfirst_cs,
to_char (clients.date_intake,'MM/DD/YY')AS Date_Created,
clients.client_id,
clients.display_intake,
-- staff.staff_name_cs, -- Line Commented out
groups.name
FROM
public.clients,
public.groups,
public.staff,
public.link_group
WHERE
-- clients.zrud_staff = staff.zzud_staff AND --Line commented out
clients.zzud_client = link_group.zrud_client AND
groups.zzud_group = link_group.zrud_group AND
clients.date_intake BETWEEN (now() - '8 days'::interval)::timestamp AND now()
ORDER BY
groups.name ASC,
clients.client_id ASC,
staff.staff_name_cs ASC
I get 173 entries
I know I need to do an outer join to capture all clients regardless of if there
is a staff assigned, but each attempt has failed. I have done outer joins with
two tables, but adding a third has twisted my brain.
Thanks for any suggestions
I have no way of testing this (or of knowing that it is right) but what I read in your query is that you want something similar to this:
SELECT --I just used short aliases. I choose something other than the table name so I know it is an alias "c" for client etc...
c.name_lastfirst_cs,
to_char (c.date_intake,'MM/DD/YY')AS Date_Created,
c.client_id,
c.display_intake,
s.staff_name_cs,
g.name,
l.zrud_client AS "link_client",--I'm selecting some data here so that I can debug later, you can just filter this out with another select if you need to
l.zzud_group AS "link_group" --Again, so I can see these relationships
FROM
public.clients c
LEFT OUTER JOIN staff s ON --is staff required? If it isn't then outer join (optional)
s.zzud_staff = c.zrud_staff --so we linked staff to clients here
LEFT OUTER JOIN public.link_group l ON --this looks like a lookup table to me so we select the lookup record
l.zrud_client = c.zzud_client -- this is how I define the lookup, a client id
LEFT OUTER JOIN public.groups g ON --then we use that to lookup a group
g.zzup_group = l.zrud_group --which is defined by this data here
WHERE -- the following must be true
c.date_intake BETWEEN (now() - '8 days'::interval)::timestamp AND now()
Now for the why: I've basically moved your where clause to JOIN x ON y=z syntax. In my experience this is a better way to write an maintain queries as it allows you to specify relationships between tables rather than doing a big-ol'-join and trying to filter that data with the where clause. Keep in mind each condition is REQUIRED not optional so when you say you want records with the following conditions you're going to get them (and if I read this right--I probably don't as I don't have a schema in-front of me) if a record is missing a link-table record OR a staff member you're going to filter it out.
Alternatively (possibly significantly slower) You can SELECT anything so you can chain it like:
SELECT
*
FROM
(
SELECT
*
FROM
public.clients
WHERE
x condition
)
WHERE
y condition
OR
SELECT * FROM x WHERE x.condition IN (SELECT * FROM y)
In your case this tactic probably won't be easier than a standard join syntax.
^And some serious opinion here: I recommend you use the join syntax I outlined above here. It is functionally the same as joining and specifying a where clause, but as you noted, if you don't understand the relationships it can cause a Cartesian join. http://www.tutorialspoint.com/sql/sql-cartesian-joins.htm . Lastly, I tend to specify what type of join I want. I write INNER JOIN and OUTER JOIN a lot in my queries because it helps the next person (usually me) figure out what the heck I meant. If it is optional use an outer join, if it is required use an inner join (default).
Good luck! There are much better SQL developers out there and there's probably another way to do it.
I have a query that uses a subquery and I am having a problem returning the expected results. The error I receive is..."Only one expression can be specified in the select list when the subquery is not introduced with EXISTS." How can I rewrite this to work?
SELECT
a.Part,
b.Location,
b.LeadTime
FROM
dbo.Parts a
LEFT OUTER JOIN dbo.Vendor b ON b.Part = a.Part
WHERE
b.Location IN ('A','B','C')
AND
Date IN (SELECT Location, MAX(Date) FROM dbo.Vendor GROUP BY Location)
GROUP BY
a.Part,
b.Location,
b.LeadTime
ORDER BY
a.Part
I think something like this may be what you're looking for. You didn't say what version of SQL Server--this works in SQL 2005 and up:
SELECT
p.Part,
p.Location, -- from *p*, otherwise if no match we'll get a NULL
v.LeadTime
FROM
dbo.Parts p
OUTER APPLY (
SELECT TOP (1) * -- * here is okay because we specify columns outside
FROM dbo.Vendor v
WHERE p.Location = v.Location -- the correlation part
ORDER BY v.Date DESC
) v
WHERE
p.Location IN ('A','B','C')
ORDER BY
p.Part
;
Now, your query can be repaired as is by adding the "correlation" part to change your query into a correlated subquery as demonstrated in Kory's answer (you'd also remove the GROUP BY clause). However, that method still requires an additional and unnecessary join, hurting performance, plus it can only pull one column at a time. This method allows you to pull all the columns from the other table, and has no extra join.
Note: this gives logically the same results as Lamak's answer, however I prefer it for a few reasons:
When there is an index on the correlation columns (Location, here) this can be satisfied with seeks, but the Row_Number solution has to scan (I believe).
I prefer the way this expresses the intent of the query more directly and succinctly. In the Row_Number method, one must get out to the outer condition to see that we are only grabbing the rn = 1 values, then bop back into the CTE to see what that is.
Using CROSS APPLY or OUTER APPLY, all the other tables not involved in the single-inner-row-per-outer-row selection are outside where (to me) they belong. We aren't squishing concerns together. Using Row_Number feels a bit like throwing a DISTINCT on a query to fix duplication rather than dealing with the underlying issue. I guess this is basically the same issue as the previous point worded in a different way.
The moment you have TWO tables from which you wish to pull the most recent value, the Row_Number() solution blows up completely. With this syntax, you just easily add another APPLY clause, and it's crystal clear what you're doing. There is a way to use Row_Number for the multiple tables scenario by moving the other tables outside, but I still don't prefer that syntax.
Using this syntax allows you to perform additional joins based on whether the selected row exists or not (in the case that no matching row was found). In the Row_Number solution, you can only reasonably do that NOT NULL checking in the outer query--so you are forced to split up the query into multiple, separated parts (you don't want to be joining to values you will be discarding!).
P.S. I strongly encourage you to use aliases that hint at the table they represent. Please don't use a and b. I used p for Parts and v for Vendor--this helps you and others make sense of the query more quickly in the future.
If I understood you corrrectly, you want the rows with the max date for locations A, B and C. Now, assuming SQL Server 2005+, you can do this:
;WITH CTE AS
(
SELECT
a.Part,
b.Location,
b.LeadTime,
RN = ROW_NUMBER() OVER(PARTITION BY a.Part ORDER BY [Date] DESC)
FROM
dbo.Parts a
LEFT OUTER JOIN dbo.Vendor b ON b.Part = a.Part
WHERE
b.Location IN ('A','B','C')
)
SELECT Part,
Location,
LeadTime
FROM CTE
WHERE RN = 1
ORDER BY Part
In your subquery you need to correlate the Location and Part to the outer query.
Example:
Date = (SELECT MAX(Date)
FROM dbo.Vender v
WHERE v.Location = b.Location
AND v.Part = b.Part
)
So this will bring back one date for each location and part
why is the query returning: ORA-00933: SQL command not properly ended and on removing the Natural keyword, it turns true(it executes)?????????
You either let Oracle do the join for you (using natural) or you do it explicitly.
Taken from Oracles documentation:
The following two statements are equivalent:
SELECT * FROM COUNTRIES NATURAL JOIN CITIES
SELECT * FROM COUNTRIES JOIN CITIES
USING (COUNTRY, COUNTRY_ISO_CODE)
You need to choose one approach or the other - at the moment you're trying to mix the two.
What about the following is not proper syntax for Postgresql?
select p.*, SUM(vote) as votes_count
FROM votes v, posts p
where p.id = v.`voteable_id`
AND v.`voteable_type` = 'Post'
group by v.voteable_id
order by votes_count DESC limit 20
I am in the process of installing postgresql locally but wanted to get this out sooner :)
Thank you
MySQL is a lot looser in its interpretation of standard SQL than PostgreSQL is. There are two issues with your query:
Backtick quoting is a MySQL thing.
Your GROUP BY is invalid.
The first one can be fixed by simply removing the offending quotes. The second one requires more work; from the fine manual:
When GROUP BY is present, it is not valid for the SELECT list expressions to refer to ungrouped columns except within aggregate functions, since there would be more than one possible value to return for an ungrouped column.
This means that every column mentioned in your SELECT either has to appear in an aggregate function or in the GROUP BY clause. So, you have to expand your p.* and make sure that all those columns are in the GROUP BY, you should end up with something like this but with real columns in place of p.column...:
select p.id, p.column..., sum(v.vote) as votes_count
from votes v, posts p
where p.id = v.voteable_id
and v.voteable_type = 'Post'
group by p.id, p.column...
order by votes_count desc
limit 20
This is a pretty common problem when moving from MySQL to anything else.