I need to join tableA, tableB, and tableC, but it's possible that tableB won't have a corresponding row. Posted below is how I am currently doing the query. The problem with it is that if tableB doesn't have a correspoinding row, it won't return a result. My sql skills are very rusty so I appreciate your help. Thanks.
SELECT [column names]
FROM tableA AS a, tableB AS b, tableC as c
WHERE b.blah = a.blah
AND c.foo = a.foo
AND [more where conditions]
Don't use the , syntax. Use JOIN to allow for a readable LEFT JOIN...
SELECT
*
FROM
tableA
LEFT JOIN
tableB
ON TableB.x = TableA.y
LEFT JOIN
tableC
ON TableC.x = TableB.y
AND TableC.y = TableA.z
Use a LEFT JOIN.
SELECT [column names]
FROM
tableA AS a
LEFT JOIN tableB AS b ON b.blah = a.blah
JOIN tableC as c ON c.foo = a.foo
SELECT [column names]
FROM tableA AS a INNER JOIN tableC as c ON (c.foo = a.foo)
LEFT OUTER JOIN tableB as B on (b.blah = a.blah)
WHERE [more where conditions]
If the [more where conditions] are on B, then you need to include them in the OUTER JOIN ON clause.
The terminology here (so you can look up more details) is an Outer Join. The other answer(s) are fine -- but watch out for whether you want an INNER or OUTER join on table c (do you want records returned if there are no matching rows in tableC)? Here is a link for the general issue.
http://www.w3schools.com/sql/sql_join_left.asp
Related
I'm trying to run this SQL Expression in Access:
Select *
From ((TableA
Left Join TableB
On TableB.FK = TableA.PK)
Left Join TableC
On TableC.FK = TableB.PK)
Left Join (SELECT a,b,c FROM TableD WHERE b > 1) AS TableD
On (TableD.FK = TableC.PK AND TableA.a = TableD.a)
but it keeps getting error: Join-Expression not supported.
Whats the problem?
Sorry, im just starting with Jet-SQL and in T-SQL its all fine.
Thanks
The issue is that the final outer join condition TableA.a = TableD.a will cause the query to contain ambiguous outer joins, since the records to which TableA is joined to TableD will depend upon the results of the joins between TableA->TableB, TableB->TableC and TableC->TableD.
To avoid this, you'll likely need to structure your query with the joins between tables TableA, TableB & TableC existing within a subquery, the result of which is then outer joined to TableD. This unambiguously defines the order in which the joins are evaluated.
For example:
select * from
(
select TableA.a, TableC.PK from
(
TableA left join TableB on TableA.PK = TableB.FK
)
left join TableC on TableB.PK = TableC.FK
) q1
left join
(
select TableD.a, TableD.b, TableD.c, TableD.FK from TableD
where TableD.b > 1
) q2
on q1.a = q2.a and q1.PK = q2.FK
Consider relating every join to the FROM table to avoid having to nest relations.
SELECT *
FROM ((TableA
LEFT JOIN TableB
ON TableB.FK = TableA.PK)
LEFT JOIN TableC
ON TableC.FK = TableA.PK)
LEFT JOIN
(SELECT FK,a,b,c
FROM TableD WHERE b > 1
) AS TableD
ON (TableD.FK = TableA.PK)
AND (TableD.a = TableA.a)
I have a following tables:
TableA
id
name
TableB
id
tableA_id
TableC
id
tableA_id
So tables B and C have tableA_id fk.
I need a query which will return all id-s from TableA that have reference in either TableB or TableC.
If I do standard join, it will return only values that have reference in both tables B and C.
I could do this using two queries, one joins B, other joins C and use UNION to merge results, but I dont want to write same query twice.
Is there a way to achieve this 'OR' JOIN??
Try with this
SELECT DISTINCT TABLEA.ID_A, TABLEA.NAME
FROM TABLEA,TABLEB,TABLEC
WHERE TABLEA.ID_A = TABLEB.ID_A AND TABLEA.ID_A = TABLEC.ID_A
Using DISTINCT TAG you eliminate duplicates.
Something like this?
SELECT
*
FROM
TableA,
TableB,
TableC
WHERE
TableA.id = TableB.tableA_id
OR TableA.id = TableC.tableA_id
You can use left outer joins and checks for the ids:
SELECT a.id FROM A a
LEFT JOIN B b ON a.id = b.tableA_id LEFT JOIN C c ON a.id = c.tableA_id
WHERE b.id IS NOT NULL OR c.id IS NOT NULL
Can anyone help me figure out the correct WHERE clause for the following scenario:
select A.name
from tableA A, tableB B
where A.id = B.id
and
(
B.field = 5
OR
B.hasNoRowForJoinedID
)
I feel like I'm missing something really obvious here in how to accomplish this, but I can't for the life of me put my finger on it.
You are using an outdated SQL Syntax. To perform the LEFT OUTER JOIN based your your request above, you can do the following:
SELECT A.name
FROM A
LEFT OUTER JOIN B ON A.id = B.id
WHERE (B.field = 5 OR B.field IS NULL)
Use proper join syntax and not the outdated ones:
select A.name
from tableA A
left join tableB B on A.id = B.id and B.field = 5
Hi I have a situation where I need to Join two tables but filter value from a third table. As below:
SELECT a.Key , (SELECT SUM(B.hours) FROM tableB as B
INNER JOIN tableC as C ON B.List=C.List
WHERE C.Status = 'Approved' AND B.Key LIKE A.key) ,
(SELECT SUM(B.hours) FROM tableB as B
INNER JOIN tableC as C ON B.List=C.List
WHERE C.Status = 'Pending' AND B.Key LIKE A.key)
FROM tableA as A GROUP BY A.key
is there another way to do this without using correlated subqueries? i'd like to use joins , but i just don't know how to link table C into this picture.
Thanks in advance.
The subquery may not be such a bad idea, but you can do this with conditional aggregation:
SELECT a.Key,
sum(iif(c.Status = "Approved", B.hours, 0)),
sum(iif(c.Status = "Pending", B.hours, 0))
FROM tableA as A left join
(tableB as b inner join
tableC as c
on b.list = c.list
)
on b.key like a.key
GROUP BY A.key;
MS Access has arcane syntax for joins, particularly for multiple joins. I think the above is correct.
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?