Is it allowed to reference external field from nested select?
E.g.
SELECT
FROM ext1
LEFT JOIN (SELECT * FROM int2 WHERE int2.id = ext1.some_id ) as x ON 1=1
in this case, this is referencing ext1.some_id in nested select.
I am getting errors in this case that field ext1.some_id is unknow.
Is it possible? Is there some other way?
UPDATE:
Unfortunately, I have to use nested select, since I am going to add more conditions to it, such as LIMIT 0,1
and then I need to use a second join on the same table with LIMIT 1,1 (to join another row)
The ultimate goal is to join 2 rows from the same table as if these were two tables
So I am kind of going to "spread" a few related rows into one long row.
The answer to your initial question is: No, remove your sub-query and put the condition into the ON-clause:
SELECT *
FROM ext1
LEFT JOIN int2 ON ( int2.id = ext1.some_id )
One solution could be to use variables to find the first (or second) row, but this solution would not work efficiently with indexes, so you might end up with performance problems.
SELECT ext1.some_id, int2x.order_col, int2x.something_else
FROM ext1
LEFT JOIN (SELECT `int2`.*, #i:=IF(#id=(#id:=id), #i+1, 0) As rank
FROM `int2`,
( SELECT #i:=0, #id:=-1 ) v
ORDER BY id, order_col ) AS int2x ON ( int2x.id = ext1.some_id
AND int2x.rank = 0 )
;
This assumes that you have a column that you want to order by (order_col) and Left Joins the first row per some_id.
Do you mean this?
SELECT ...
FROM ext1
LEFT JOIN int2 ON int2.id=ext1.some_id
That's what the ON clause is for:
SELECT
FROM ext1
LEFT JOIN int2 AS x ON x.id = ext1.some_id
Related
I'm going to create a data model in oracle fusion applications. I need to create column End_date based on two tables in the query. So I used two methods.
Using a subquery:
SELECT *
FROM (SELECT projects_A.end_date
FROM projects_A, projects_B
WHERE projects_A.p_id = projects_B.p_id
AND rownum = 1)
Using a LEFT OUTER JOIN:
SELECT projects_A.end_date
FROM projects_A
LEFT JOIN projects_B
ON projects_A.p_id = projects_B.p_id
WHERE rownum = 1
Here when I used a subquery, the query returns the results as expected. But when I use left outer join with WHERE rownum = 1 the result is zero. Without WHERE rownum = 1 it retrieves all the results. But I want only the first result. So how can I do that using left outer join? Thank you.
Looks like you want to bring a non-null end_date value(So, add NULLS LAST), but the sorting order is not determined yet(you might add a DESC to the end of the ORDER BY clause depending on this fact ), and use FETCH clause(the DB version is 12c+ as understood from the comment) with ONLY option to exclude ties as yo want to bring only single row.
So, you can use the following query :
SELECT A.end_date
FROM projects_A A
LEFT JOIN projects_B B
ON A.p_id = B.p_id
ORDER BY end_date NULLS LAST
FETCH FIRST 1 ROW ONLY
I am trying to select all notes that have a status of completed.
Notes are stored in there own table where we have a note status history table with a foreign key relationship by noteId. How can I get the data from the table referenced in the WHERE clause (t2) to that I do not have to loop again through the results just to get the data for CompletedBy.
SELECT DISTINCT
t1.NoteId,
t2.CompletedBy-- error
FROM
Note t1
WHERE
EXISTS
(
SELECT
TOP 1 *
FROM
NoteStatus t2
WHERE
t1.NoteId = t2.NoteId
AND t2.Completed = 1
)
You seem to want a lateral join:
select n.noteId, ns.completedBy
from note n
cross apply (
select top (1) *
from notestatus ns
where ns.noteId = n.noteId and ns.completed = 1
) ns
You could get the same result with a correlated subquery - but the lateral join gives you the opportunity to return more columns fro the notestatus table, if you ever need to.
distinct does not seem to make sense, so I removed it - you can add it back if that's really needed for some reason you did not explain.
You can use an explicit join or -- more simply -- a lateral join:
SELECT n.NoteId, ns.CompletedBy-- error
FROM Note n CROSS APPLY
(SELECT TOP 1 ns.*
FROM NoteStatus ns
WHERE ns.NoteId = n.NoteId AND
ns.Completed = 1
);
I'm not sure why you would need SELECT DISTINCT, so I removed it. A column called NoteId sure seems like the primary key in a table calld Note.
I am trying to select records from a temp table based on another temp table which holds their previous statuses (StatusHistory).
So if the record doesn't exist in the status table, then it should be selected. If the status of the record is different than the one in the StatusHistory table, then the record should be selected. Otherwise, if it exists with the same status in the StatusHistory table, then it should be ignored.
I have this SQL but it doesn't seem to be the best solution. Can you please point me to a better way to achieve that assuming that there are thousands of records in the tables? Would it be possible to achieve the same result with a JOIN statement?
SELECT AI.item
FROM #AllItems AI
WHERE NOT EXISTS (
SELECT * FROM #StatusHistory HS
WHERE HS.itemId = AI.itemId
) OR NOT AI.itemStatus IN ( SELECT HS.itemStatusHistory
FROM #StatusHistory HS
WHERE HS.itemId = AI.itemId
AND HS.itemId = AI.itemId )
Yes, you can do this with a LEFT JOIN.
SELECT AI.item
FROM #AllItems AI
LEFT JOIN #StatusHistory HS ON AI.itemId = HS.itemId
AND AI.itemStatus = HS.itemStatusHistory
WHERE HS.itemId IS NULL
A better solution, however, is to use NOT EXISTS:
SELECT AI.item
FROM #AllItems AI
WHERE NOT EXISTS
(
SELECT 1 FROM #StatusHistory SH
WHERE SH.itemId = AI.itemId
AND SH.itemStatusHistory = AI.itemStatus
);
As pointed out by Aaron, this usually performs better than a LEFT JOIN.
I am trying to get information from 3 tables in my database. I am trying to get 4 fields. 'kioskid', 'kioskhours', 'videotime', 'sessiontime'. In order to do this, i am trying a join in a subquery. This is what I have so far:
SELECT k.kioskid, k.hours, v.time, s.time
FROM `nsixty_kiosks` as k
LEFT JOIN (SELECT time
FROM `nsixty_videos`
ORDER BY videoid) as v
ON kioskid = k.kioskid LEFT JOIN
(SELECT kioskid, time
FROM `sessions`
ORDER BY pingid desc LIMIT 1) as s ON s.kioskid = k.kioskid
WHERE hours is NOT NULL
When I run this query, it works but it shows every row instead of just showing the last row of each kiosk id. Which is meant to show based on the line 'ORDER BY pingid desc LIMIT 1'.
Any body have some ideas?
Instead of joining to s, you can use a correlated subquery:
SELECT k.kioskid,
k.hours,
v.time,
( SELECT time
FROM sessions
WHERE sessions.kioskid = k.kioskid
ORDER
BY pingid DESC
LIMIT 1
)
FROM nsixty_kiosks AS k
LEFT
JOIN ( SELECT time
FROM `nsixty_videos`
ORDER BY videoid
) AS v
ON kioskid = k.kioskid
WHERE hours IS NOT NULL
;
N.B. I didn't fix your LEFT JOIN (...) AS v, because I don't understand what it's trying to do, but it too is broken; the ON clause doesn't refer to any of its columns, and there's no point in having an ORDER BY in a subquery unless you also have a LIMIT or whatnot in there.
Well, your join on the 'v' subquery doesn't actually reference the 'v' subquery, nor does the 'v' subquery even contain a kioskid field to JOIN on, so that's undoubtedly part of the problem.
To go much further we'd need to see schema and sample data.
I am trying to filter a single table (master) by the values in multiple other tables (filter1, filter2, filter3 ... filterN) using only joins.
I want the following rules to apply:
(A) If one or more rows exist in a filter table, then include only those rows from the master that match the values in the filter table.
(B) If no rows exist in a filter table, then ignore it and return all the rows from the master table.
(C) This solution should work for N filter tables in combination.
(D) Static SQL using JOIN syntax only, no Dynamic SQL.
I'm really trying to get rid of dynamic SQL wherever possible, and this is one of those places I truly think it's possible, but just can't quite figure it out. Note: I have solved this using Dynamic SQL already, and it was fairly easy, but not particularly efficient or elegant.
What I have tried:
Various INNER JOINS between master and filter tables - works for (A) but fails on (B) because the join removes all records from the master (left) side when the filter (right) side has no rows.
LEFT JOINS - Always returns all records from the master (left) side. This fails (A) when some filter tables have records and some do not.
What I really need:
It seems like what I need is to be able to INNER JOIN on each filter table that has 1 or more rows and LEFT JOIN (or not JOIN at all) on each filter table that is empty.
My question: How would I accomplish this without resorting to Dynamic SQL?
In SQL Server 2005+ you could try this:
WITH
filter1 AS (
SELECT DISTINCT
m.ID,
HasMatched = CASE WHEN f.ID IS NULL THEN 0 ELSE 1 END,
AllHasMatched = MAX(CASE WHEN f.ID IS NULL THEN 0 ELSE 1 END) OVER ()
FROM masterdata m
LEFT JOIN filtertable1 f ON join_condition
),
filter2 AS (
SELECT DISTINCT
m.ID,
HasMatched = CASE WHEN f.ID IS NULL THEN 0 ELSE 1 END,
AllHasMatched = MAX(CASE WHEN f.ID IS NULL THEN 0 ELSE 1 END) OVER ()
FROM masterdata m
LEFT JOIN filtertable2 f ON join_condition
),
…
SELECT m.*
FROM masterdata m
INNER JOIN filter1 f1 ON m.ID = f1.ID AND f1.HasMatched = f1.AllHasMatched
INNER JOIN filter2 f2 ON m.ID = f2.ID AND f2.HasMatched = f2.AllHasMatched
…
My understanding is, filter tables without any matches simply must not affect the resulting set. The output should only consist of those masterdata rows that have matched all the filters where matches have taken place.
SELECT *
FROM master_table mt
WHERE (0 = (select count(*) from filter_table_1)
OR mt.id IN (select id from filter_table_1)
AND (0 = (select count(*) from filter_table_2)
OR mt.id IN (select id from filter_table_2)
AND (0 = (select count(*) from filter_table_3)
OR mt.id IN (select id from filter_table_3)
Be warned that this could be inefficient in practice. Unless you have a specific reason to kill your existing, working, solution, I would keep it.
Do inner join to get results for (A) only and do left join to get results for (B) only (you will have to put something like this in the where clause: filterN.column is null) combine results from inner join and left join with UNION.
Left Outer Join - gives you the MISSING entries in master table ....
SELECT * FROM MASTER M
INNER JOIN APPRENTICE A ON A.PK = M.PK
LEFT OUTER JOIN FOREIGN F ON F.FK = M.PK
If FOREIGN has keys that is not a part of MASTER you will have "null columns" where the slots are missing
I think that is what you looking for ...
Mike
First off, it is impossible to have "N number of Joins" or "N number of filters" without resorting to dynamic SQL. The SQL language was not designed for dynamic determination of the entities against which you are querying.
Second, one way to accomplish what you want (but would be built dynamically) would be something along the lines of:
Select ...
From master
Where Exists (
Select 1
From filter_1
Where filter_1 = master.col1
Union All
Select 1
From ( Select 1 )
Where Not Exists (
Select 1
From filter_1
)
Intersect
Select 1
From filter_2
Where filter_2 = master.col2
Union All
Select 1
From ( Select 1 )
Where Not Exists (
Select 1
From filter_2
)
...
Intersect
Select 1
From filter_N
Where filter_N = master.colN
Union All
Select 1
From ( Select 1 )
Where Not Exists (
Select 1
From filter_N
)
)
I have previously posted a - now deleted - answer based on wrong assumptions on you problems.
But I think you could go for a solution where you split your initial search problem into a matter of constructing the set of ids from the master table, and then select the data joining on that set of ids. Here I naturally assume you have a kind of ID on your master table. The filter tables contains the filter values only. This could then be combined into the statement below, where each SELECT in the eligble subset provides a set of master ids, these are unioned to avoid duplicates and that set of ids are joined to the table with data.
SELECT * FROM tblData INNER JOIN
(
SELECT id FROM tblData td
INNER JOIN fa on fa.a = td.a
UNION
SELECT id FROM tblData td
INNER JOIN fb on fb.b = td.b
UNION
SELECT id FROM tblData td
INNER JOIN fc on fc.c = td.c
) eligible ON eligible.id = tblData.id
The test has been made against the tables and values shown below. These are just an appendix.
CREATE TABLE tblData (id int not null primary key identity(1,1), a varchar(40), b datetime, c int)
CREATE TABLE fa (a varchar(40) not null primary key)
CREATE TABLE fb (b datetime not null primary key)
CREATE TABLE fc (c int not null primary key)
Since you have filter tables, I am assuming that these tables are probably dynamically populated from a front-end. This would mean that you have these tables as #temp_table (or even a materialized table, doesn't matter really) in your script before filtering on the master data table.
Personally, I use the below code bit for filtering dynamically without using dynamic SQL.
SELECT *
FROM [masterdata] [m]
INNER JOIN
[filter_table_1] [f1]
ON
[m].[filter_column_1] = ISNULL(NULLIF([f1].[filter_column_1], ''), [m].[filter_column_1])
As you can see, the code NULLs the JOIN condition if the column value is a blank record in the filter table. However, the gist in this is that you will have to actively populate the column value to blank in case you do not have any filter records on which you want to curtail the total set of the master data. Once you have populated the filter table with a blank, the JOIN condition NULLs in those cases and instead joins on itself with the same column from the master data table. This should work for all the cases you mentioned in your question.
I have found this bit of code to be faster in terms of performance.
Hope this helps. Please let me know in the comments.