For simplicity; I have three tables: A, B and C
A: {ID, Value, Group}
B: {ID, Description}
C: {ID, Date}
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:
SELECT A.Value, A.Group, B.Description, C.Date
FROM A LEFT JOIN B ON A.ID = B.ID
LEFT JOIN C ON A.ID = C.ID
Basically, the joins need to be of the form A LEFT JOIN B and A LEFT JOIN C
so that I can get all the required info even with missing IDs.
What is the best way to do this in SQL?
Related
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 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
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.
I have 4 tables , A,B,C,D.
A stores my Customer Id , B ,C D stores various details of customer.
For Eg. B stores Education ,C stores Occupation , D stores Interests.
Now a Customer may have not have entry in C ,D or It may have entry in B and D but not in C.
I want to select all the information by joing all the four tables. Customer_id is present in all the four tables. Inner join will clearly not work.
I am thinking of Left outer join. Could someone help me with the requirement.
An LEFT OUTER JOIN will only get the rows where column A:B match or B:C match, if u want to keep the values of certain rows from table C, D in blank u can first make an
LEFT OUTER JOIN WITH A and B and then make a full outer join with C and D, in that way u are going to be able to keep all the data from C and D no mather if the have or not values in it
I am thinking in somethin like this:
SELECT a.store, b.education, d.storeinterest FROM
(
SELECT * FROM A
LEFT OUTER JOIN B
ON A = B
) A
FULL OUTER JOIN C
ON A = C
FULL OUTER JOIN D
ON A= D
Something along these lines should get you started:
SELECT a.*, b.*, c.*, d.*
FROM a LEFT OUTER JOIN b on
a.customer_id = b.customer_id LEFT OUTER JOIN c
on a.customer_id = c.customer_id LEFT OUTER JOIN d
on a.customer_id = d.customer_id
Ok so I will try to simplify the problem that I have.
I have 4 tables:
TableA:
OneID
TableB:
OneID (FK to TableA)
TwoID (FK to TableC)
TableC:
TwoID
ThreeID (FK to TableD)
TableD:
ThreeID
I need a query to retrieve data from all 4 of these tables.
The query criteria is:
want to inner join tables A, B, C
want to join above result with table D with the following conditions:
if a record is in Table D but not in Table C, then it must always be present in the results
otherwise if a record is in Table D and Table C, then it should only be present if it is in the result of the A,B,C join
The scenario you have described is not really possible (or at least they are not really logical)
if a record is in Table D but not in Table C, then it must always be present in the results
The only way a record could be "in Table D and not in Table C" is if the foreign key is null in table D, with no link from table D to tables A or B there is no other way you could define a record as being present in D and not in C:
otherwise if a record is in Table D and Table C, then it should only be present if it is in the result of the A,B,C join
Again, the only way this could happen is with NULLABLE foreign keys. Regardless I think any of the below will get you the results you require:
SELECT A.OneID, B.TwoID, c.ThreeID, D.FourID
FROM D
LEFT JOIN (C
INNER JOIN B
ON B.TwoID = C.TwoID
INNER JOIN A
ON A.OneID = B.OneID)
ON C.ThreeID = D.ThreeID;
Or
SELECT A.OneID, B.TwoID, c.ThreeID, D.FourID
FROM A
INNER JOIN B
ON B.OneID = A.OneID
INNER JOIN C
ON C.TwoID = B.TwoID
RIGHT JOIN D
ON D.ThreeID = C.ThreeID
Or
SELECT A.OneID, B.TwoID, c.ThreeID, D.FourID
FROM A
INNER JOIN B
ON B.OneID = A.OneID
INNER JOIN C
ON C.TwoID = B.TwoID
INNER JOIN D
ON D.ThreeID = C.ThreeID
UNION ALL
SELECT NULL, NULL, NULL, FourID
FROM D
WHERE ThreeID IS NULL;
Examples on SQL Fiddle
The first two have the same execution plan, it is just a matter of preference, I personally dislike using RIGHT JOIN because it makes queries feel like they in the wrong order i.e bottom to top, but this is purely my preference. The last query may perform better depending on the cardinality of your data and any indexes you have
EDIT
With your revised criteria I think the easiest way to implement this is with a UNION ALL:
SELECT A.OneID, B.TwoID, c.ThreeID, d3 = D.ThreeID
FROM A
INNER JOIN B
ON B.OneID = A.OneID
INNER JOIN C
ON C.TwoID = B.TwoID
INNER JOIN D
ON D.ThreeID = C.ThreeID
UNION ALL
SELECT NULL, NULL, NULL, ThreeID
FROM D
WHERE NOT EXISTS (SELECT 1 FROM C WHERE C.ThreeID = D.ThreeID);
Example on SQL Fiddle
I am not 100% sure I understood you correctly but I will try to help anyway. It seems that you need to do FULL OUTER JOIN on table D:
SELECT
*
FROM
TableA AS A INNER JOIN
TableB AS B ON B.A_Id = A.Id INNER JOIN
TableC AS C ON C.B_Id = B.Id FULL OUTER JOIN
TableD AS D ON D.C_Id = C.Id
If I have misunderstood your requirements and you need more complicated criteria, you could just do FULL OUTER JOIN on all the tables and put extra conditions in WHERE part:
SELECT
*
FROM
TableA AS A FULL OUTER JOIN
TableB AS B ON B.A_Id = A.Id FULL OUTER JOIN
TableC AS C ON C.B_Id = B.Id FULL OUTER JOIN
TableD AS D ON D.C_Id = C.Id
WHERE
--if a record is in Table D but not in Table C, then it must always be present in the results
(D.Id IS NOT NULL AND C.Id IS NULL) OR
(
--otherwise if a record is in Table D and Table C, then it should only be present if it is in the result of the A,B,C join
(D.Id IS NOT NULL AND C.Id IS NOT NULL) AND
--want to inner join tables A, B, C
(A.Id IS NOT NULL AND B.Id IS NOT NULL AND B.Id IS NOT NULL)
)