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Oracle "(+)" Operator
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I'm trying to convert some Oracle SQL code to regular SQL and am having trouble with the numerous variables in the SELECT statement, tables in the FROM statement, and (+) WHERE statements.
I have looked through similar posts but all provide simple examples with just 2 variables, 2 tables, and 1 (+) WHERE statement. I'm not sure how to apply what I'm seeing from the other forum posts to multiple variables, tables, and (+) WHERE statements.
SELECT
a.ID,
c.var1,
d.var2
FROM a, b, c, d, x, y
WHERE a.ID(+) = b.ID
AND c.var1(+) = b.var1
AND x.id(+) = y.id;
I tried to convert all the (+) WHERE statements to LEFT JOINs as shown below. I did 3 LEFT JOINS, one for each (+) WHERE statement:
SELECT
a.ID,
c.var1,
d.var2
FROM a, b, c, d, x, y
WHERE b.ID in
(SELECT b.ID
FROM b
LEFT JOIN a
ON a.ID = b.ID)
The query:
SELECT a.ID,
c.var1,
d.var2
FROM a, b, c, d, x, y
can be rewritten using ANSI-join syntax as:
SELECT a.ID,
c.var1,
d.var2
FROM a
CROSS JOIN b
CROSS JOIN c
CROSS JOIN d
CROSS JOIN x
CROSS JOIN y
If you add in the WHERE clause then WHERE c.var1(+) = b.var1 converts the CROSS JOIN to a LEFT OUTER JOIN from b to c. Similarly for the other join conditions.
Which gives you:
SELECT a.ID,
c.var1,
d.var2
FROM b
LEFT OUTER JOIN a ON a.ID = b.ID
LEFT OUTER JOIN c ON c.var1 = b.var1
CROSS JOIN d
CROSS JOIN y
LEFT OUTER JOIN x ON x.id = y.id;
fiddle
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 am trying to SELECT a few things from tables A,B, and C, but when I try to LEFT JOIN, I keep getting an error. My code currently looks like this:
FROM (A LEFT JOIN B ON A.id = B.id), C
Am I not allowed to left join two tables and include the entirety of a third?
Thanks for your help.
EDIT
Here is a sample code:
SELECT A.ID, A.place, A.receipt, D.State, A.service, B.Description, C.ID, C.receipt, C.Source
FROM B, (A LEFT JOIN C ON A.receipt = C.receipt), D;
Access doesn't support combining cross-joins with other joins, so you will have to do the left join in a subquery, and then the cross-join:
FROM (SELECT * FROM A LEFT JOIN B ON A.id = B.id) As D, C
This is more of a curiosity than an actual applied question. Say you have a statement with multiple joins such as:
SELECT
a.name,
b.salary,
c.x
FROM
[table1] a
INNER JOIN [table2] b
ON a.key = b.key
INNER JOIN [table3] c
ON b.key = c.key
Now, say you were to make several more joins to other tables whose schema was unfamiliar, however you know:
the keys on which to make the join
that several of those tables has a column with the the name 'x'.
Is it possible to select 'x' from all tables that contain it, without explicitly referring to the table alias. So it would ave a similar results as this (if it were possible)
SELECT
a.name,
b.salary,
*.x
...
No this isn't possible.
You can use a.* to get all columns from a but it is not valid to use a wildcard as the table name.
#Martin Smith is correct that you can't use *.x and refer to columns from multiple tables. There is however a way to write a query that shows all columns x from tables where they exist without breaking if one or more of the tables do not have such column. It's a rather complicated way that (mis)uses scope resolution.
Lets say that some of the tables (b and d in the example) have a column named x, while some others (c here) do not have such column. Then you can replace INNER joins with CROSS APPLY and LEFT joins with OUTER APPLY and a query with:
SELECT
a.name,
a.salary,
b.x AS bx,
'WITHOUT column x' AS cx,
d.x AS dx
FROM
a
INNER JOIN b
ON a.aid = b.aid
LEFT JOIN c
ON a.aid = c.aid
LEFT JOIN d
ON a.aid = d.aid ;
would be written as:
SELECT
a.name,
a.salary,
bx,
cx,
dx
FROM
( SELECT a.*,
'WITHOUT column x' AS x
FROM a
) a
CROSS APPLY
( SELECT x AS bx
FROM b
WHERE a.aid = b.aid
) b
OUTER APPLY
( SELECT x AS cx
FROM c
WHERE a.aid = c.aid
) c
OUTER APPLY
( SELECT x AS dx
FROM d
WHERE a.aid = d.aid
) d ;
Tested at SQL-Server 2008: SQL-Fiddle
If i write a sql:
select *
from a,b
where a.id=b.id(+)
and b.val="test"
and i want all records from a where corresponding record in b does not exist or it exists with val="test", is this the correct query?
You're much better off using the ANSI syntax
SELECT *
FROM a
LEFT OUTER JOIN b ON( a.id = b.id and
b.val = 'test' )
You can do the same thing using Oracle's syntax as well but it gets a bit hinkey
SELECT *
FROM a,
b
WHERE a.id = b.id(+)
AND b.val(+) = 'test'
Note that in both cases, I'm ignoring the c table since you don't specify a join condition. And I'm assuming that you don't really want to join A to B and then generate a Cartesian product with C.
Move the condition into the JOIN clause and use the ANSI standard join pattern.
SELECT NameYourFields,...
FROM A
LEFT OUTER JOIN B
ON A.ID = B.ID
AND B.VAL = 'test'
INNER JOIN C
ON ...
A LEFT OUTER JOIN is one of the JOIN operations that allow you to specify a join clause. It preserves the unmatched rows from the first (left) table, joining them with a NULL row in the shape of the second (right) table.
So you can do as follows :
SELECT
FROM a LEFT OUTER JOIN b
ON a.id = b.id
--Note that you have used double quote "test" which is not used for varchar in SQL you should use single quote 'test'
AND b.val = 'test';
SELECT * FROM abc a, xyz b
WHERE a.id = b.id
AND b.val = 'test'
I try to do a 3-table join in Access and it will not work. Is it possible?
I once had a problem when I tried
select
x,
y
from
A inner join
B on k=l inner join
C on f=g
This didn't work. But it works with parantheses:
select
x,
y
from (
A inner join
B on k=l ) inner join
C on f=g
All the various types of multi-table joins that are available in other flavour of SQL are permitted in MS-Access/Jet. For example, here's a straight three-table hierarchical example (a bit more real-world than the other answers here):
SELECT
x.FirstName,
x.Surname,
r.RegionName,
c.CountryName
FROM
(Customer x LEFT JOIN Region r
ON r.ID=x.RegionID)
LEFT JOIN Country c
ON c.ID=r.CountryID
Or did you want to know how to do it using the Visual Designer in MS-Access?
Yes, it's possible:
Select *
From A, B, C
Where A.a = B.b
And A.c = C.c
or
Select *
From A, B, C
Where A.a = B.b
And B.c = C.c
Access can do most types of joins (apart from a full outer) I wonder with your 3 table join if you are doing an ambiguous outer join? Have a look at this KB article for an explanation
support.microsoft.com/kb/124937