I have three tables (a, b, c) and two (b and c) need to be joined to get detail data from the first table a. But the problem is that I need to do this in one query.
If I join both tables in the same query than no records are found as detail data is either in b or c, but never in both.
To further complicate things, I need to further join other tables (b2, c2) based on with the record found is from b or c.
I am using MS SQL.
The query I have now is:
select a.*, b.name1, c.name1, b2.url, c2.url
left join b on a.aID = b.aID
left join c on a.aID = c.aID
inner join b2 on b.bID = b2.bID
inner join c2 on c.cID = c2.cID
where a.date > '9/1/2016'
I searched for a few days, but no one seems to need to go after the fourth and fifth tables in the query and so couldn't find any similar answer
Is there any way to do this? Performance is not an issue as the number of records will be less than 1,000 after executing a where clause that will always limit the records from table a.
A series of left joins with inner joins as subqueries should do the trick. The subqueries pull the b/b2 and c/c2 data together for reference in the left joins with a:
select a.*, b.name1, c.name1, b2join.url, c2join.url
FROM a
LEFT JOIN b
on a.aID = b.aID
LEFT JOIN c
on a.aID = c.aID
LEFT JOIN
(SELECT b.aID, b.bID, b2.url
FROM b
INNER JOIN b2
on b.bID = b2.bID) as b2join
on b2join.aID = a.aID
LEFT JOIN
(SELECT c.aID, c.cID, c2.url
FROM c
INNER JOIN c2
on c.cID = c2.cID) as c2join
on c2join.aID = a.aID
I think a Left Join will do it, at least for the first part:
select a.*, b.name1, c.name1
left join b on a.aID = b.aID
left join c on a.aID = c.aID
where a.date > '9/1/2016'
You will get c.name1 null when data is in b table, and b.name1 will be null when data is in c table.
For the other two joins and not sure but left join could also work.
I think, it is more simple and brief way to get the same result:
select a.*, b.name1, c.name1, b2join.url, c2join.url
FROM a
LEFT JOIN b on a.aID = b.aID
LEFT JOIN c on a.aID = c.aID
LEFT JOIN b as b2join on b2join.bID = b.bID
LEFT JOIN a as c2join on c2join.cID = c.cID
Related
I would like to ask the difference between the following join expressions and in what conditions is Method 2 more preferred than Method 1.
You can imagine tables a, b and c to be CTEs for i.e. With a AS (xxxxx), b AS (xxxxx), and c AS (xxxxx).
Method 1:
Select
a.customerid,
b.customerage,
b.customermobile,
a.itemid,
c.itemname
from a
LEFT JOIN b on
a.customerid = b.customerid
LEFT JOIN c on
a.itemid = c.itemid
Method 2:
Select
a.customerid,
b.customerage,
b.customermobile,
a.itemid,
c.itemname
from ((( a
LEFT JOIN b on
(a.customerid = b.customerid))
LEFT JOIN c on
(a.itemid = c.itemid))
There is no difference. This structure:
from a left join
b left join
c
is exactly defined as
from (a left join
b
) left join
c
(I'm leaving out the on clauses to simplify the explanation.)
Note: The order of evaluation is important for outer joins. But even for inner joins, the above is subtly different from:
from a left join
(b left join
c
)
For instance, this won't even parse if the on clause between b and c references a as well.
I have problem getting values from tables.
I need something like this
A.Id a1
B.Id b1
C.Id c1
B.Id b2
C.Id c2
C.Id c3
C.Id c4
Table A and B are joined together and also table B and C.
Table A can have one/zero or more values from table B. Same situation is for values from table C.
I need to perform left join on table A over table B and inside that left join on table B over table C.
I tried with left join from table A and B, but don't know how to perform left join inside that left join.
Is that possible? What would syntax for that look like?
edit:
Data would look like this
ZZN1 P1 NULL
ZZN1 P2 NAB1
ZZN2 P3 NAB2
ZZN2 P3 NAB3
No need to nest the left joins, you can simply flatten them and let your RDMBS handle the logic.
Sample schema:
a(id)
b(id, aid) -- aid is a foreign key to a(id)
c(id, bid) -- bid is a foreign key to b(id)
Query:
select a.id, b.id, c.id
from a
left join b on b.aid = a.id
left join c on c.bid = b.id
If the first left join does not succeed, then the second one cannot be performed either, since joining column b.id will be null. On the other hand, if the first left join succeeds, then the second one may, or may not succeed, depending if the relevant bid is available in c.
SELECT A.Name, B.Name , C.Name
FROM A
LEFT JOIN B ON A.id = B.id
LEFT JOIN C ON B.id = C.id
I have come across a Join Error in Access SQL, when using multiple "ON" criteria's. I am unable to perform an ON clause on 2 different tables, for example:
select *
from
(((A
left join B on a.id = b.id)
left join c on c.id = b.id)
left join D
on (d.id = b.id) and (d.id = a.id)
That final join statement causes an error because I link table D on table B first, and then link Table D on Table A. If I choose to instead link table D on Table B again, then it resolves. However, I need to join it this way due to the certain data I need to link Table D on from both tables.
How can I more efficiently structure my query to achieve my results?
you may try this select * from A left join B on a.id = b.id left join c on c.id = b.id left join D on d.id = b.id and d.id = a.id
It's somewhat difficult to tell what you're trying to do exactly, but most likely, this is what you want:
select *
from
(((A
left join B on a.id = b.id)
left join C on c.id = b.id)
left join D on d.id = a.id)
Since you're trying a LEFT JOIN, there is no reason to link multiple ids to eachother.
I have 5 tables: A, B, C, D, E
A: {ID, Value, GroupID, FilterID, In_Date}
B: {ID, Description, Out_Date, From_Date }
C: {ID, Category}
D: {GroupID, GroupName}
E: {FilterID, FilterName}
There could be missing IDs in B and C as a result, I'm trying to do a LEFT JOIN to get the required info. In my dataset, I've explicitly added a row in A with ID that's not in B or C. I expect it to be picked up in the following query, but it doesn't happen. I believe I'm going wrong in the WHERE clause due to null values in B and C.
SELECT A.Value, A.Group, B.Description, C.Category, D.GroupName, E.FilterName
FROM A LEFT JOIN B ON A.ID = B.ID
LEFT JOIN C ON A.ID = C.ID,
D,E
WHERE
B.Out_Date>A.In_Date,
A.GroupID=D.GroupID,
A.FilterID=E.FilterID
How can I fix this to retrieve the fields I want with null values when the ID is not in B or C , but in A?
1) Don't mix old comma separated join syntax with modern explicit join syntax!
2) When left join, put the right side table's conditions in the ON clause to get true left join behavior. (When in WHERE you get inner join result.)
SELECT A.Value, A.Group, B.Description, C.Category, D.GroupName, E.FilterName
FROM A LEFT JOIN B ON A.ID = B.ID AND B.Out_Date > A.In_Date
LEFT JOIN C ON A.ID = C.ID
JOIN D ON A.GroupID = D.GroupID
JOIN E ON A.FilterID = E.FilterID
Value and Group are reserved words in ANSI SQL, so you may need to delimit them, as "Value" and "Group".
First point: You shouldn't mix join syntaxes, just use explicit syntax.
Because of your where clause, you effectively turn your left joins in inner joins. You are probably looking for:
SELECT A.Value, A.Group, B.Description, C.Category, D.GroupName, E.FilterName
FROM A
LEFT JOIN B
ON A.ID = B.ID
AND B.Out_Date > A.In_Date
LEFT JOIN C
ON A.ID = C.ID
INNER JOIN D
ON A.GroupID = D.GroupID
INNER JOIN E
ON A.FilterID = E.FilterID
You can use this query for your problem.
SELECT A.Value, A.Group, B.Description, C.Category, D.GroupName, E.FilterName
FROM A
LEFT JOIN B
ON A.ID = B.ID
AND B.Out_Date > A.In_Date
LEFT JOIN C
ON A.ID = C.ID
LEFT JOIN D
ON A.GroupID = D.GroupID
LEFT JOIN E
ON A.FilterID = E.FilterID
Here is your table details
A: {ID, Value, GroupID, FilterID, In_Date}
B: {ID, Description, Out_Date, From_Date }
C: {ID, Category}
D: {GroupID, GroupName}
E: {FilterID, FilterName}
now you try to retrieve data using left join
so you try the flowing script
SELECT A.Value, A.Group, B.Description, C.Category, D.GroupName,E.FilterName from A left join B on A.ID=B.ID
left Join C on A.ID=C.ID
Left Join D on A.GroupID=D.GroupID
Left Join E on A.FilterID=E.FilterID
where B.Out_Date>A.In_Date
I hope this is help full for you.
Say I have 3 tables. TableA, TableB, TableC
I need to operate the recordset that is available after a INNER JOIN.
Set 1 -> TableA INNER JOIN TableB
Set 2 -> TableC INNER JOIN TableB
I need the Set 1 irrespective of if Set 2 is empty or not (LEFT OUTER JOIN) comes to mind.
So essentially, I am trying to write a query and have come this far
SELECT *
FROM TableA
INNER JOIN TableB ON ...
LEFT OUTER JOIN (TableC INNER JOIN TableB)
How would I write in SQL Server?
EDIT: In reality, what I am trying to do is to join multiple tables. How would your response change if I need to join multiple tables ex: OUTER JOIN OF (INNER JOIN of TableA and TableB) and (INNER JOIN OF TableC and TableD) NOTE: There is a new TableD in the equation
SELECT * FROM TableA
INNER JOIN TableB ON TableB.id = TableA.id
LEFT JOIN TABLEC ON TABLEC.id = TABLEB.id
I Don't know what columns you are trying to use but it is just that easy
Edit:
Looking at your edit it seems that you are confused about what Joins actually do. In the example I have written above you will recieve the following results.
Columns -> You will get all of the columns for TableA,TableB and TableC
Rows-> You will start off with all of the rows from tableA. Next you will remove all rows from TableA that do not have a matching "id" in Table B.(You will have duplicates if it is not a 1:1 relationship between TableA and TableB).
Now if you take the results from above you will match any records from TableC that match the TableB.id column. Any rows from above that do not have a matching TableC record will get a null value for all of the columns from TableC in the results.
ADVICE- I am betting that only part of this made sense to you but my advice is that you start writing some queries, predict the results and then see if your predictions are correct to see if you understand what it is doing.
What you want isn't a JOIN but a UNION.
SELECT * FROM TableA INNER JOIN TableB ON ...
UNION
SELECT * FROM TableC INNER JOIN TableD ON ...
You can actually add an ordering to your joins just like in a math equation where you might do this: (5 + 4) * (3 + 1).
Given the second part of your question, give this a try:
SELECT
<your columns>
FROM
(TableA INNER JOIN Table B ON <join criteria for A to B>)
LEFT OUTER JOIN
(TableC INNER JOIN Table D ON <join criteria for C to D>) ON
<join criteria for AxB to CxD>
Select * from ((((TableA a inner join TableB b on a.id = b.id)
left outer join TableC c on b.id = c.id)
full outer join TableD d on c.id = d.id)
right outer join TableE e on e.id = d.id)
/* etc, etc... */
You can lose the brackets if you want.
try this..
SELECT *
FROM TableA a
INNER JOIN TableB b ON a.id=b.id
LEFT OUTER JOIN (SELECT *
FROM TableC c
INNER JOIN TableD d on c.id=d.id
) dt on b.id=dt.id
You didn't give your join conditions or explain how the tables are intended to be related, so it's not obvious how this might be simplified.
SELECT a.a_id, b1.b_id b1_id, b2_id, bc.c_id
FROM TableA a JOIN TableB b1 on a.b_id = b1.b_id
LEFT JOIN (SELECT c.c_id, b2.b_id b2_id
FROM TableC c JOIN TableB b2 ON c.b_id = b2.b_id
) bc ON bc.c_id = a.c_id;
Looking at your latest edit, you can do something along the lines of:
SELECT <columns>
FROM (SELECT <columns> FROM TableA JOIN TableB ON <A-B join conditions>)
LEFT JOIN
(SELECT <columns> FROM TableC JOIN TableD ON <C-D join conditions>)
ON <AB-CD join conditions>
Although you don't actually need the inner projections, and can do:
SELECT <columns>
FROM (TableA a JOIN TableB b ON <A-B join conditions>)
LEFT JOIN
(TableC c JOIN TableD d ON <C-D join conditions>)
ON <AB-CD join conditions>
Where the AB-CD join conditions are written in terms of columns of a, b, c, d etc directly.
Since you're using Sql Server, why not create views that help you? Stuffing everything in a gigantic Sql statement can become hard to read. An example view might look like:
create view AandB
as
select *
from A
inner join B on B.aid = A.aid
And the same for CandD. Then you can retrieve the optional join with simple Sql:
select *
from AndB
left outer join CandD on AndB.cid = CandD.cid
If you're interested in rows from both sets, you can do a full join:
select *
from AndB
full outer join CandD on AndB.cid = CandD.cid
Assuming I Understand your question, I think this is what you're asking for:
SELECT *
FROM TableA INNER JOIN TableB on TableA.JoinColumn = TableB.JoinColumn
LEFT OUTER JOIN TableC on TableB.JoinColum = TableC.JoinColumn
INNER JOIN TableD on TableC.JoinColumn = TableD.JoinColumn
Note that the JoinColumn used to join A & B doesn't necesarilly have to be the same column as the one used to join B & C, and so on for C & D.
SELECT *
FROM TableA A
INNER JOIN TableB B ON B.?? = A.?? AND ...
LEFT JOIN TableC C ON C.?? = B.?? AND ...
LEFT JOIN TableB B2 ON B2.?? = C.?? AND ...
LEFT JOIN TableD D ON D.?? = C.?? AND ...
So here's the thing: logically, joins aren't actually between specific tables, they are between a table and the rest of the "set" (of joins and tables). So while you know that there is a 1-to-1 relationship between C and B2 or between C and D, you can't INNER JOIN to C because C could be null from it's LEFT JOIN to B, which will eliminate those rows, effectively undoing your LEFT join.
So basically, any joins to a table that's LEFT outer joined must also be LEFT outer joined. Does this make sense?