I am doing some relational algebra exercizes. On a teacher slide I saw a thing that makes me think that there can be an error.
I think, the third JOIN, should be
JOIN 'Farmacia' as F
ON 'D'.'idCF' = 'F'.'idFì
instead of
JOIN 'Farmacia' as F
ON 'F'.'idFì = 'D'.'idCF'
Using this last command you will join Farmacia on itself, isn't it?
The slide question says:
Which pharmacy does sell drug X of phramaceutic company Y?
The order of the columns in the ON part of the statement doesn't influence how the JOIN itself is done.
This:
SELECT t1.columnA, t2.columnB
FROM Table1 t1
JOIN Table2 t2 ON t1.ID = t2.ID
will yield the same results as this:
SELECT t1.columnA, t2.columnB
FROM Table1 t1
JOIN Table2 t2 ON t2.ID = t1.ID
The self-join you described would have been something like this:
SELECT t1.columnA, t2.columnB
FROM Table1 t1
JOIN Table1 t2 ON t1.managerID = t2.employeeID
Related
I have two tables t1 & t2. In t1, there are 1641787 records. In t2, there are 33176007 records. I want to take two columns from table2 and keep everything of t1. When I use left join with t1 to t2, I got more records than t1. I would like to get a similar number of records as t1 after joining. Please give me a suggestion. Here is my code:
SELECT t1.*,
t2.City
FROM t1
LEFT JOIN
t2
ON t1.ID = t2.ID;
You can aggregate and choose an arbitrary value:
select t1.*, t2.city
from t1 left join
(select t2.id, any_value(t2.city) as city
from t2
group by t2.id
) t2
on t1.id = t2.id;
I'm looking to do what I believe is a double-nested check across three tables, but have no idea how to do so.
I have Table1, Table2, and Table3.
All are tied by an ID and a "Longform" and "Shortform" in Table1:
I'm trying to find:
Entries whose IDs appear in Table2 that have the same Longform as those in Table3, but don't share the same Shortform.
This is about as far as I've gotten:
SELECT T2.Longform,T2.Shortform FROM(
SELECT Table1.Longform,Table1.Shortform,Table1.ID FROM OuterTable1.Table1
LEFT JOIN OuterTable2.Table2 on Table1.ID = Table2.ID)
WHERE Table2.ID IS NOT NULL) T2
;
I know I'm probably going to have to do another nested select, or a join, on Outertable3.Table3 but I'm not sure which... Or where...
Any help appreciated as always.
Try the following:
Select *
(
Select T1.*
from T2
inner join T1
on T1.ID = T2.ID
) as Tab
inner join
(
Select T1.*
from T3
inner join T1
on T1.ID = T3.ID
) as Tab2
on Tab.id = Tab2.id
and Tab.Longform = Tab2.Longform
and Tab.Shortform <> Tab2.Shortform
To get the longform join table1 to table2 or table3. Then use EXISTS to check in a subquery if the IDs of table1 are different but the longform is equal.
SELECT *
FROM table2 t21
INNER JOIN table1 t11
ON t11.id = t21.id
WHERE EXISTS (SELECT *
FROM table3 t32
INNER JOIN table1 t12
ON t12.id = t32.id
WHERE t12.id <> t11.id
AND t12.longform = t11.longform);
Assuming ID is unique in all three tables
Select t2.id,t2.shortform, t1.shortform AS shortformTab1, t2.longform
FROM table2 t2
JOIN table3 t3
ON t2.id = t3.id AND t2.longform = t3.longform
JOIN table1 t1
ON t2.id = t1.id AND t2.shortform != t1.shortform
I'm trying to JOIN 2 tables ON a key like
SELECT column1,column2
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.t2id = t2.id
Now, I have a 3rd table that has a Foreign Key with t2's id that I want to join... When I do
LEFT JOIN
Table3 t3 ON t3.t2id = --<-------------- This is where I'm lost
I don't know if I should do ON t3.t2id = t1.t2id OR ON t3.t2id = t2.id
What I need is the list of t2ids which are still in the picture after the first join. However, it seems as though if I specify either of the above, it will just pull ids from the original table before the first join?
To clarify one more time: I'm trying to essentially do a INNER JOIN of Table1 and Table2, get the resulting table, then get the t2ids of those results and feed them into a final join such that the final result contains all of Table3's rows as well as the data from the first join
You said: "final result contains all of Table3's rows as well as the data from the first join".
It means that you need
Table3 LEFT JOIN <previous results>
instead of
<previous results> LEFT JOIN Table3
The easiest way to write it is to use Common-Table Expressions:
WITH
CTE_InnerJoin
AS
(
SELECT column1, column2, t1.t2id
FROM
Table1 t1
INNER JOIN Table2 t2 ON t1.t2id = t2.id
)
SELECT
CTE_InnerJoin.column1
,CTE_InnerJoin.column2
,Table3....
FROM
Table3
LEFT JOIN CTE_InnerJoin ON CTE_InnerJoin.t2id = Table3.t2id
;
It doesn't matter what column you include in the CTE: t1.t2id or t2.id, the values in them are the same, because they are inner-joined together.
JOINs already do exactly what you want. A JOIN isn't always between two tables. Frequently, it's between the results of previous joins.
SELECT column1,column2
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.t2id = t2.id
LEFT JOIN
Table3 t3 ON t3.t2id = t2.id
At the point at which you're writing the final ON clause here, what you're joining is precisely the results of the previous INNER JOIN on the left and the table Table3 on the right. All of t1, t2 and t3 are in scope within the ON clause, but note that t1 and t2 are now both used as aliases into the same source of rows - the previous INNER JOIN.
As a further example, consider the "diamond join":
SELECT
*
FROM
t1
left join
t2
on
t1.a = t2.b
left join
t3
on
t1.c = t3.d
inner join
t4
on
t2.e = t4.f OR
t3.g = t4.h
This is a way of joining two tables (t1 and t4) based on two alternative joins. Note that in the final inner join, what is on the "left" is the result of already joining tables t1, t2 and t3.
Join the table having foreign key with
Try this....
SELECT column1,column2
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.t2id = t2.id
LEFT join Table3 t3 ON t2.id=t3.t2id
Or Like this.
SELECT t12.column1 ,
t12.column2 ,
t3.*
FROM (
--- INNER JOIN of Table1 and Table2, get the resulting table,
SELECT t1.column1 ,
t2.column2 ,
t1.t2id --- or t2.id doesn't matter because its inner join
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.t2id = t2.id
) T12
LEFT JOIN Table3 T3 ON t3.t2id = t1.t2id --- then get the t2ids of those results
--- and feed them into a final join
--- if you want to get all rows from Table3, Change LEFT JOIN Table3 T3 ON t3.t2id = T1.t2id
--- into RIGHT JOIN Table3 T3 ON t3.t2id = T1.t2id
try this
select t3.*, column1, column2
from
table1 t1 inner join table2 t2 on t1.t2id = t2.id
right outer join table3 t3 on t3.t2id = t2.id
equvalent to
select t3.*, column1, column2
from
table1 t1 inner join table2 t2 on t1.t2id = t2.id
right outer join table3 t3 on t3.t2id = t1.t2id
if you want all rows from table 3 and those matching rows from table1 inner joined to table2 then you can use this syntax:
select t3.*,
column1, column2
from table3 t3
left join table2 t2
inner join table1 t1
on t1.t2id = t2.id
on t3.t2id = t2.id
select t.* from table1 t where t.id NOT IN(
select Id from t2 where usrId in
(select usrId from t3 where sId=value));
I the result i need is like if there are matching id's in t1 and t2 then those id's should be omitted and only the remaining rows should be given to me. I tried converting into join but it is giving me the result i wanted. Below is my join query.
SELECT t.* FROM table1 t JOIN table2 t2 ON t.Id <> t2.Id
JOIN table3 t3 ON t3.Id=t2.Id WHERE t3.sId= :value
This doesn't feth me the correct result. it was returning all the rows, but i want to restrict the result based on the matching id's in table t1 and table t2. Matching id's should be ommited from the result.I will be passing the value for sId.
I believe this to be an accurate refactor of your query using joins. I don't know if we can do away with the subquery, but in any case the logic appears to be the same.
select t1.*
from table1 t1
left join
(
select t2.Id
from table2 t2
inner join table3 t3
on t2.usrId = t3.usrId
where t3.sId = <value>
) t2
on t1.Id = t2.Id
where t2.Id is null
Let's break down and solve problem step by step.
So your query
select t.* from table1 t where t.id NOT IN(
select Id from t2 where usrId in
(select usrId from t3 where sId=value));
on converting the inner query to JOIN will yield
select t.* from table1 t where t.id NOT IN
(SELECT T2.ID FROM T2 JOIN T3 on T2.UsrID =T3.UsrID and T3.sID=value)
which on further converting to JOIN with outer table will be
select t.* from table1 t LEFT JOIN
(SELECT T2.ID FROM T2 JOIN T3 on T2.UsrID =T3.UsrID and T3.sID=value)t4
ON t.id =T4.ID
WHERE t4.ID is NULL
In case you completely want to remove sub-query you can try like this
SELECT t.*
FROM table1 t
LEFT JOIN T2
ON T.ID=T2.ID
LEFT JOIN T3
ON T3.UsrId=T2.UsrID AND T3.sId=value
WHERE T3.UsrID IS NULL
I want to use the result of a FULL OUTER JOIN as a table to FULL OUTER JOIN on another table. What is the syntax that I should be using?
For eg: T1, T2, T3 are my tables with columns id, name. I need something like:
T1 FULL OUTER JOIN T2 on T1.id = T2.id ==> Let this be named X
X FULL OUTER JOIN T3 on X.id = t3.id
I want this to be achieved so that in the final ON clause, I want the T3.id to match either T1.id or T2.id. Any alternative way to do this is also OK.
SELECT COALESCE(X.id,t3.id) AS id, *-- specific columns here instead of the *
FROM
(
SELECT COALESCE(t1.id,t2.id) AS id, * -- specific columns here instead of the *
FROM T1 FULL OUTER JOIN T2 on T1.id = T2.id
) AS X
FULL OUTER JOIN T3 on X.id = t3.id
Often, chains of full outer joins don't behave quite as expected. One replacements uses left join. This works best when a table has all the ids you need. But you can also construct that:
from (select id from t1 union
select id from t2 union
select id from t3
) ids left join
t1
on ids.id = t1.id left join
t2
on ids.id = t2.id left join
t3
on ids.id = t3.id
Note that the first subquery can often be replaced by a table. If you have such a table, you can select the matching rows in the where clause:
from ids left join
t1
on ids.id = t1.id left join
t2
on ids.id = t2.id left join
t3
on ids.id = t3.id
where t1.id is not null or t2.id is not null or t3.id is not null
You can do it like you suggested, using IN()
FROM T1
FULL OUTER JOIN T2
ON(T1.id = T2.id)
FULL OUTER JOIN T3
ON(T3.ID IN(T2.id,T1.id))
or I think you can do it with a UNION (depends on what you need) :
SELECT * FROM
(SELECT name,id from T1
UNION
SELECT name,id from T2) x
FULL OUTER JOIN T3
ON(t3.id = x.id)