I am trying to map a self join where the right table must be filtered, e.g. SQL such as this:
select t2.* from table t
left join table t2
on t2.parentID = t.ID and t2.active=1;
I can figure out the syntax if I wanted to filter the left table:
// works
var query = from t in table
where t.active= 1
join t2 in table
on t.parentID equals t2.ID into joined
from r in joined.DefaultIfEmpty() ...
But I can't figure out how to filter the right table. It seems like it should be something like this...
// does not work
var query = from t in table
join t2 in table
where t.field = 1
on t.parentID equals t2.ID into joined
from r in joined.DefaultIfEmpty() ...
(not valid... join can't have where). There is discussion of using multiple from clauses, but if I create more than one from clause, so I can add a where to the 2nd one, I can't figure out how to join the results of them into a new temporary table.
I can't just add a "where" after the join; the right table must be filtered first or matches will occur, and a where clause at the end would remove the row from the left table that I do want in the output. That is, the output should have rows where there's nothing matched from filtered right table. So I need to filter the right table before the join.
I think you are looking to do this:
var query = from t in table
join t2 in
(from t3 in table
where t3.field = 1
select t3)
on t.parentID equals t2.ID into joined
from r in joined.DefaultIfEmpty() ...
Another way is to use multiple from like this:
var query = from t in table
from t2 in table.Where(x => x.field = 1)
.Where(x => x.ID == t.parentID)
.DefaultIfEmpty()
select ....
Related
I have three table, table_1 (id), table_2(id), table_pivot(tbl1_id, tbl2_id). When I use query like this:
select *
from public.table_1 t1
left join public.table_pivot tp on tp.tbl1_id = t1.id and tp.user_id = 1
left join public.table_2 t2 on t2.id = tp.tbl2_id;
Data from table_1 is show. But when I use where condition. Like this:
select *
from public.table_1 t1
left join public.table_pivot tp on tp.tbl1_id = t1.id
left join public.table_2 t2 on t2.id = tp.tbl2_id
where tp.user_id = 1;
Data from table_1 not show.
I hope advance can help explain why?
Thanks.
Including a where clause on an outer joined table, effectively converts the join into an inner join. If there are no matching values in table_pivot, then
you will get no results at all. This is standard sql.
I have two table with one of them is vertical i.e store only key value pair with ref id from table 1. i want to join both table and dispaly key value pair as a column in select. and also perform sorting on few keys.
T1 having (id,empid,dpt)
T2 having (empid,key,value)
select
T1.*,
t21.value,
t22.value,
t23.value,
t24.value
from Table1 t1
join Table2 t21 on t1.empid = t21.empid
join Table2 t22 on t1.empid = t22.empid
join Table2 t23 on t1.empid = t23.empid
where
t21.key = 'FNAME'
and t22.key = 'LNAME'
and t23.key='AGE'
The query you demonstrate is very inefficient (another join for each additional column) and also has a potential problem: if there isn't a row in T2 for every key in the WHERE clause, the whole row is excluded.
The second problem can be avoided with LEFT [OUTER] JOIN instead of [INNER] JOIN. But don't bother, the solution to the first problem is a completely different query. "Pivot" T2 using crosstab() from the additional module tablefunc:
SELECT * FROM crosstab(
'SELECT empid, key, value FROM t2 ORDER BY 1'
, $$VALUES ('FNAME'), ('LNAME'), ('AGE')$$ -- more?
) AS ct (empid int -- use *actual* data types
, fname text
, lname text
, age text);
-- more?
Then just join to T1:
select *
from t1
JOIN (<insert query from above>) AS t2 USING (empid);
This time you may want to use [INNER] JOIN.
The USING clause conveniently removes the second instance of the empid column.
Detailed instructions:
PostgreSQL Crosstab Query
My basic question has to do with updating multiple columns at once from specified values in my query. The reason I want to do this is that I am updating my values from a ginormous table so I only want to query it once in order to reduce run time. Here is an example of an example select statement that returns the value I want for just one of the columns I need to update:
select a.Value
from Table1
left outer join
(
select ID, FilterCol1, FilterCol2, Value
from Table2
) a on a.ID = Table1.ID
where {Condition1a on FilterCol1}
and {Condition2a on FilterCol2}
In order to update multiple columns at once I would like to be able do something like this (but it returns NULL):
Update T1
set T1Value1 = (select a.Value where {Condition1a on FilterCol1}
and {Condition2a on FilterCol2)
,T1Value2 = (select a.Value where {Condition1b on FilterCol1}
and {Condition2b on FilterCol2})
from Table1 T1
left outer join
(
select ID, FilterCol1, FilterCol2, Value
from Table2
) a on a.ID = Table1.ID
Any help figuring this out would be greatly appreciated, let me know if you have any questions or if I made any errors. Thanks!
EDIT: I think I have identified the problem, but I'm not sure of a solution yet. I think seeing the issue requires a little more context: The select from table 2 is actually an unpivot on a wide table. This means that when the left outer join is applied, there will be multiple rows for a given ID. What the case statement that Earl suggested seems to be doing (and I assume this is happening with the where clause as well) is comparing my Conditions to only the first row of the columns from a. Since my conditions are meant to help determine which of the rows from a is chosen, they will always evaluate false for the first row (I know this just from what I know about the data), hence my perpetual NULL values. Does anyone know of a workaround to look at the other rows in a?
UPDATE T1
SET T1Value1 = CASE WHEN (FilterCol1 = Condition1a AND FilterCol2 = Condition2a) THEN a.Value END,
T1Value2 = CASE WHEN (FilterCol1 = Condition1b AND FilterCol2 = Condition2b) THEN a.Value END
FROM Table1 T1
left outer join
(
select ID, FilterCol1, FilterCol2, Value
) a on a.ID = Table1.ID
How would I redesign the below query so that it will recursively loop through entire tree to return all descendants from root to leaves? (I'm using SSMS 2008). We have a President at the root. under him are the VPs, then upper management, etc., on down the line. I need to return the names and titles of each. But this query shouldn't be hard-coded; I need to be able to run this for any selected employee, not just the president. This query below is the hard-coded approach.
select P.staff_name [Level1],
P.job_title [Level1 Title],
Q.license_number [License 1],
E.staff_name [Level2],
E.job_title [Level2 Title],
G.staff_name [Level3],
G.job_title [Level3 Title]
from staff_view A
left join staff_site_link_expanded_view P on P.people_id = A.people_id
left join staff_site_link_expanded_view E on E.people_id = C.people_id
left join staff_site_link_expanded_view G on G.people_id = F.people_id
left join facility_view Q on Q.group_profile_id = P.group_profile_id
Thank you, this was most closely matching what I needed. Here is my CTE query below:
with Employee_Hierarchy (staff_name, job_title, id_number, billing_staff_credentials_code, site_name, group_profile_id, license_number, region_description, people_id)
as
(
select C.staff_name, C.job_title, C.id_number, C.billing_staff_credentials_code, C.site_name, C.group_profile_id, Q.license_number, R.region_description, A.people_id
from staff_view A
left join staff_site_link_expanded_view C on C.people_id = A.people_id
left join facility_view Q on Q.group_profile_id = C.group_profile_id
left join regions R on R.regions_id = Q.regions_id
where A.last_name = 'kromer'
)
select C.staff_name, C.job_title, C.id_number, C.billing_staff_credentials_code, C.site_name, C.group_profile_id, Q.license_number, R.region_description, A.people_id
from staff_view A
left join staff_site_link_expanded_view C on C.people_id = A.people_id
left join facility_view Q on Q.group_profile_id = C.group_profile_id
left join regions R on R.regions_id = Q.regions_id
WHERE C.STAFF_NAME IS NOT NULL
GROUP BY C.STAFF_NAME, C.job_title, C.id_number, C.billing_staff_credentials_code, C.site_name, C.group_profile_id, Q.license_number, R.region_description, A.people_id
ORDER BY C.STAFF_NAME
But I am wondering what is the purpose of the "Employee_Hierarchy"? When I replaced "staff_view" in the outer query with "Employee_Hierarchy", it only returned one record = "Kromer". So when/where can we use "Employee_Hierarchy"?
See:
SQL Server - Simple example of a recursive CTE
MSDN: Recursive Queries using Common Table Expression
SQL Server recursive CTE (this seems pretty much like exactly what you are working on!)
Update:
A proper recursive CTE consist of basically three things:
an anchor SELECT to begin with; that can select e.g. the root level employees (where the Reports_To is NULL), or it can select any arbitrary employee that you define, e.g. by a parameter
a UNION ALL
a recursive SELECT statement that selects from the same, typically self-referencing table and joins with the recursive CTE being currently built up
This gives you the ability to recursively build up a result set that you can then select from.
If you look at the Northwind sample database, it has a table called Employees which is self-referencing: Employees.ReportsTo --> Employees.EmployeeID defines who reports to whom.
Your CTE would look something like this:
;WITH RecursiveCTE AS
(
-- anchor query; get the CEO
SELECT EmployeeID, FirstName, LastName, Title, 1 AS 'Level', ReportsTo
FROM dbo.Employees
WHERE ReportsTo IS NULL
UNION ALL
-- recursive part; select next Employees that have ReportsTo -> cte.EmployeeID
SELECT
e.EmployeeID, e.FirstName, e.LastName, e.Title,
cte.Level + 1 AS 'Level', e.ReportsTo
FROM
dbo.Employees e
INNER JOIN
RecursiveCTE cte ON e.ReportsTo = cte.EmployeeID
)
SELECT *
FROM RecursiveCTE
ORDER BY Level, LastName
I don't know if you can translate your sample to a proper recursive CTE - but that's basically the gist of it: anchor query, UNION ALL, recursive query
I have a stored procedure which is running quite slow. Therefore I want to extract some of the query in a separate view.
My code looks something like this:
DECLARE #tmpTable TABLE(..)
INSERT INTO #tmpTable (..) *query* (returns 3000 rows)
Select ... from table1
inner join table2
inner join table3
inner join #tmpTable
...
I then extract (copy-paste) the *query* and put it in a view - i.e. vView.
Doing this will then give me a different result:
Select ... from table1
inner join table2
inner join table3
inner join vView
...
Why? I can see that the vView and the #tmpTable both returns 3000 rows, so they should match (also did a except query to check).
Any comments would be much appriciated as I feel quite stuck with this..
EDITED:
This is the full query for getting the result (using #tmpTable or vView gives me different results, although the appear the same):
select dep.sid as depsid, dep.[name], COUNT(b.sid) as possiblelogins, count(ls.clientsid) as logins
from department dep
inner join relationship r on dep.sid=r.primarysid and r.relationshiptypeid=27 and r.validto is null
inner join [user] u on r.secondarysid=u.sid
inner join relationship r2 on u.sid=r2.secondarysid and r2.validto is null and r2.relationshiptypeid in (1,37)
inner join client c on r2.primarysid=c.sid
inner join ***#tmpTable or vView*** b on b.sid = c.sid
left outer join (select distinct clientsid from logonstatistics) as ls on b.sid=ls.clientsid
GROUP BY dep.sid, dep.[name],dep.isdepartment
HAVING dep.isdepartment=1
You maybe don't need the view/table if you change to this.
It joins on to client c and appears to be there only to JOIN onto logonstatistics
--remove inner join ***#tmpTable or vView*** b on b.sid = c.sid
--change JOIN
left outer join (select distinct clientsid from logonstatistics) as ls on c.sid=ls.clientsid
And change COUNT(b.sid) to COUNT(c.sid) in the SELECT clause
Otherwise, if you get different results you have two options I can see:
Table and view have different data. Have you run a line by line comparsion?
One has NULL, one has a value (especially for the sid column which will affect the JOIN)
Finally, when you says "different results" do you mean you get x2 or x3 rows? A different COUNT? What?