Hopefully someone can show me how to complete my sql. I'll start by showing you my existing query:
Select a.ID, a.NAME,
CASE When b.SOURCE = Value1 then 'Rename1'
When b.SOURCE = Value2 then 'Rename2'
When b.SOURCE = etc. ....
END,
b.TARGET, b.COMPARE
FROM Table'a', Table'b'
WHERE b.SOURCE in(Value1, Value2, Value...etc)
AND (a.ID = b.ID_1 or a.ID = b.ID_2)
Now my issue is my client wants to look up 3 different tables (each table contains primary key = a.ID) and return the values from only the column values that are referenced in the Case Statement above.
I assume I would need to do a join but not sure how to go about it. Any suggestions?
Thanks!
Puckhog
Following is the sample query:
Select T1.column,T2.Column,T3.Column
From Table1 T1
Join Table2 T2
on T1.MatchingColumn=T2.MatchingColumn
Join Table3 T3
on T2.MatchingColumn=T3.MatchingColumn
You could do something like this?
SELECT
a.ID, a.NAME, c.SOMETHING
FROM
a
JOIN
b
ON a.ID = b.ID
JOIN
c
ON a.ID = c.ID
WHERE [conditions]
Related
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You are using an outdated SQL Syntax.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Use proper join syntax and not the outdated ones: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
I have next tables.
First one is A.
A have two columns: A_ID and A_VALUE.
Second table is B. B too have two columns: B_ID and B_VALUE
In additional I have table C. Table C have C_ID and bool columns C_BOOL
If C_BOOL value == true i need select value from A with given ID.
If C_BOOL value == false i need select value from B.
How I can write SELECT for this?
I use oracle db.
Thanks in advice.
SELECT CASE C.BOOL WHEN 1 THEN A.ID ELSE B.ID END
FROM A
JOIN B
ON B.ID = A.ID
JOIN C
ON C.ID = A.ID
Try this query:
SELECT C_ID,CASE WHEN C_BOOL = 1 THEN T3.A_VALUE ELSE T2.B_VALUE END
FROM TABLE_C T1 LEFT OUTER JOIN TABLE_B T2 ON T1.C_ID = T2.B_ID
LEFT OUTER JOIN TABLE_A T3 T2 ON T1.C_ID = T3.A_ID
select decode(C.BOOL,1,A.ID,B.ID) FROM C
JOIN A
ON A.ID=C.ID
JOIN B
ON B.ID=C.ID;
I consider T McKeown answer as valid this is just equivalent (but more compact) I suppose.
This is evidently correct syntax in SQL Server:
SELECT a.id, b.name
FROM Table1 a, Table2 b
WHERE a.id = b.fk1
So is this:
SELECT a.id, c.status
FROM Table1 a
JOIN Table3 c ON a.id = c.fk2
But this apparently isn't:
SELECT a.id, b.name, c.status
FROM Table1 a, Table2 b
JOIN Table3 c ON a.id = c.fk2
WHERE a.id = b.fk1
I would NOT normally want to construct a query in the third case's style (and really not the first case's either), but it would probably be the path of least resistence in editing some code that's already been written at my company. Somebody used the first form with five different tables, and I really need to work in a sixth table through a JOIN statement, without taking chances of messing up what they already have. Even though I could re-write their stuff outright if I need to, I would really like to know how to do something like in the third case.
Running the code exactly as-is in the examples, the third case gives me this error message:
The multi-part identifier "a.id" could not be bound.
What is syntactically breaking the third case? What simple fix could be applied? Thanks!
I, likewise, would not recommend doing this. But, you can just change the , to a cross join:
SELECT a.id, b.name, c.status
FROM Table1 a cross join Table2 b
JOIN Table3 c ON a.id = c.fk2
WHERE a.id = b.fk1
This code:
SELECT a.id, b.name, c.status
FROM Table1 a, Table2 b
JOIN Table3 c ON a.id = c.fk2
WHERE a.id = b.fk1
is doing a cross join on a and the result of an inner join on b and c. c cannot access any of the fields in a because the join is being performed on b. what you should do is change your query to:
SELECT a.id, b.name, c.status
FROM Table1 a
inner join Table2 b on a.id = b.fk1
inner JOIN Table3 c ON a.id = c.fk2
I have a long stored procedure and I would like to make a slight modification to the procedure without having to create a new one(for maintenance purposes).
Is it possible to use a IF or CASE in the FROM statement of the select statement to join other tables?
Like this:
from tableA a
join tableB b a.indexed = c.indexed
IF #Param='Y'
BEGIN
join tableC c a.indexed = c.indexed
END
It didn't seem to work for me. But I am wondering if this is even possible and/or if this even makes sense to do.
Thanks.
No, it is not possible. You can only accomplish this through the use of dynamic SQL.
The Curse and Blessings of Dynamic SQL
An Intro to Dynamic SQL
I would not advise using Dynamic SQL, there are most likely better ways to perform this operation but you would have to provide more info.
You can achieve something like it if you have a left outer join
Consider
declare #param bit = 1
select a.*, b.*, c.* from a
inner join b on a.id = b.a_id
left outer join c on b.id = c.b_id and #param = 1
This will return all columns from a, b, c.
Now try with
declare #param bit = 0
This will return all columns from a and b, and nulls for columns of c.
It won't work if both joins are inner.
No this is not possible. Your best bet would probably be to select from both tables and only include the data your care about. If you provide an example of what you are trying to do I can provide a better answer.
Attempt at an example:
SELECT t1.id, COALESCE(t2.name, t3.name)
FROM Table1 as t1
LEFT JOIN Table2 as t2
ON t1.id = t2.id
LEFT JOIN Table2 as t3
ON t1.id = t3.id
While what you proposed is not possible, you can play with your where conditions:
from tableA a
inner join tableB b ON a.indexed = c.indexed
left join tableC c ON a.indexed = c.indexed AND 1 = CASE #Param WHEN 'Y' THEN 1 ELSE 0 END
More performant would be to just doing a big
IF #Param='Y' THEN
from tableA a
inner join tableB b ON a.indexed = c.indexed
ELSE
from tableA a
inner join tableB b ON a.indexed = c.indexed
left join tableC c ON a.indexed = c.indexed
You haven't revealed you SELECT clause. The essence of what you want is as follows:
SELECT indexed
FROM tableA
INTERSECT
SELECT indexed
FROM tableB
INTERSECT
SELECT indexed
FROM tableC
WHERE #Param = 'Y'
Then use this table expression as dictated by your SELECT clause e.g. say you only want to project tableA:
WITH T
AS
(
SELECT indexed
FROM tableA
INTERSECT
SELECT indexed
FROM tableB
INTERSECT
SELECT indexed
FROM tableC
WHERE #Param = 'Y'
)
SELECT *
FROM tableA
WHERE indexed IN ( SELECT indexed FROM T );
I need to simulate the left join effect without using the "left join" key.
I have two tables, A and B, both with id and name columns. I would like to select all the dbids on both tables, where the name in A equals the name in B.
I use this to make a synchronization, so at the beginning B is empty (so I will have couples with id from A with a value and id from B is null). Later I will have a mix of couples with value - value and value - null.
Normally it would be:
SELECT A.id, B.id
FROM A left join B
ON A.name = B.name
The problem is that I can't use the left join and wanted to know if/how it is possible to do the same thing.
you can use this approach, but you must be sure that the inner select only returns one row.
SELECT A.id,
(select B.id from B where A.name = B.name) as B_ID
FROM A
Just reverse the tables and use a right join instead.
SELECT A.id,
B.id
FROM B
RIGHT JOIN A
ON A.name = B.name
I'm not familiar with java/jpa. Using pure SQL, here's one approach:
SELECT A.id AS A_id, B.id AS B_id
FROM A INNER JOIN B
ON A.name = B.name
UNION
SELECT id AS A_id, NULL AS B_id
FROM A
WHERE name NOT IN ( SELECT name FROM B );
In SQL Server, for example, You can use the *= operator to make a left join:
select A.id, B.id
from A, B
where A.name *= B.name
Other databases might have a slightly different syntax, if such an operator exists at all.
This is the old syntax, used before the join keyword was introduced. You should of course use the join keyword instead if possible. The old syntax might not even work in newer versions of the database.
I can only think of two ways that haven't been given so far. My last three ideas have already been given (boohoo) but I put them here for posterity. I DID think of them without cheating. :-p
Calculate whether B has a match, then provide an extra UNIONed row for the B set to supply the NULL when there is no match.
SELECT A.Id, A.Something, B.Id, B.Whatever, B.SomethingElse
FROM
(
SELECT
A.*,
CASE
WHEN EXISTS (SELECT * FROM B WHERE A.Id = B.Id) THEN 1
ELSE 0
END Which
FROM A
) A
INNER JOIN (
SELECT 1 Which, B.* FROM B
UNION ALL SELECT 0, B* FROM B WHERE 1 = 0
) B ON A.Which = B.Which
AND (
A.Which = 0
OR (
A.Which = 1
AND A.Id = b.Id
)
)
A slightly different take on that same query:
SELECT A.Id, B.Id
FROM
(
SELECT
A.*,
CASE
WHEN EXISTS (SELECT * FROM B WHERE A.Id = B.Id) THEN A.Id
ELSE -1 // a value that does not exist in B
END PseudoId
FROM A
) A
INNER JOIN (
SELECT B.Id PseudoId, B.Id FROM B
UNION ALL SELECT -1, NULL
) B ON A.Which = B.Which
AND A.PseudoId = B.PseudoId
Only for SQL Server specifically. I know, it's really a left join, but it doesn't SAY LEFT in there!
SELECT A.Id, B.Id
FROM
A
OUTER APPLY (
SELECT *
FROM B
WHERE A.Id = B.Id
) B
Get the inner join then UNION the outer join:
SELECT A.Id, B.Id
FROM
A
INNER JOIN B ON A.name = B.name
UNION ALL
SELECT A.Id, NULL
FROM A
WHERE NOT EXISTS (
SELECT *
FROM B
WHERE A.Id = B.Id
)
Use RIGHT JOIN. That's not a LEFT JOIN!
SELECT A.Id, B.Id
FROM
B
RIGHT JOIN A ON B.name = A.name
Just select the B value in a subquery expression (let's hope there's only one B per A). Multiple columns from B can be their own expressions (YUCKO!):
SELECT A.Id, (SELECT TOP 1 B.Id FROM B WHERE A.Id = B.Id) Bid
FROM A
Anyone using Oracle may need some FROM DUAL clauses in any SELECTs that have no FROM.
You could use subqueries, something like:
select a.id
, nvl((select b.id from b where b.name = a.name), "") as bId
from a
you can use oracle + operator for left join :-
SELECT A.id, B.id
FROM A , B
ON A.name = B.name (+)
Find link :-
Oracle "(+)" Operator
SELECT A.id, B.id
FROM A full outer join B
ON A.name = B.name
where A.name is not null
I'm not sure if you just can't use a LEFT JOIN or if you're restricted from using any JOINS at all. But as far as I understand your requirements, an INNER JOIN should work:
SELECT A.id, B.id
FROM A
INNER JOIN B ON A.name = B.name
Simulating left join using pure simple sql:
SELECT A.name
FROM A
where (select count(B.name) from B where A.id = B.id)<1;
In left join there are no lines in B referring A so 0 names in B will refer to the lines in A that dont have a match
+ or A.id = B.id in where clause to simulate the inner join