What is the difference between an inner join and outer join? What's the precise meaning of these two kinds of joins?
Check out Jeff Atwood's excellent:
A Visual Explanation of SQL Joins
Marc
Wikipedia has a nice long article on the topic [here](http://en.wikipedia.org/wiki/Join_(SQL))
But basically :
Inner joins return results where there are rows that satisfy the where clause in ALL tables
Outer joins return results where there are rows that satisfy the where clause in at least one of the tables
You use INNER JOIN to return all rows from both tables where there is a match. ie. in the resulting table all the rows and columns will have values.
In OUTER JOIN the resulting table may have empty columns. Outer join may be either LEFT or RIGHT
LEFT OUTER JOIN returns all the rows from the first table, even if there are no matches in the second table.
RIGHT OUTER JOIN returns all the rows from the second table, even if there are no matches in the first table.
INNER JOIN returns rows that exist in both tables
OUTER JOIN returns all rows that exist in either table
Inner join only returns a joined row if the record appears in both table.
Outer join depending on direction will show all records from one table, joined to the data from them joined table where a corresponding row exists
Using mathematical Set,
Inner Join is A ^ B;
Outer Join is A - B.
So it is (+) is your A side in the query.
Assume an example schema with customers and order:
INNER JOIN: Retrieves customers with orders only.
LEFT OUTER JOIN: Retrieves all customers with or without orders.
RIGHT OUTER JOIN: Retrieves all orders with or without matching customer records.
For a slightly more detailed infos, see Inner and Outer Join SQL Statements
Related
I have 2 queries in big query where i want to join 2 tables in some condition.
First query
Second query is same but im using JOIN instead of LEFT JOIN.
Can anyone explain me why LEFT JOIN with WHERE condition returns diffrent results count then INNER JOIN?
why LEFT JOIN with WHERE condition returns diffrent results count then INNER JOIN?
They are considering different starting sets to work with. Here are some nice illustrations on difference between joins:
https://www.diffen.com/difference/Inner_Join_vs_Outer_Join
https://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins
Relevant images from referenced urls are here:
note that OUTER is optional so left outer join is equal to left join
I am joining 2 tables on the first table I get all the relevant data on the second table I only get nulls. There are no nulls in either table Can any one tell me why this is happening?
select * from apmast
left join apitem
on apmast.fvendno + apmast.fccompany = apitem.fcinvkey
There is a problem with your ON that's resulting in you not getting matching records. A LEFT JOIN means that you should get all data from the left table and only the matching records from the right table, or else NULL where there are no matching records. The key to the join, however, is the ON statement. Make sure that apmast.fvendno + apmast.fccompany is actually equal to apitem.fcinvkey.
here is a explanation on the types of joins just incase you get stuck in the future.
INNER JOIN this will get only the rows that match in both the FROM clause and the JOINING table.
LEFT OUTER JOIN this gets all the rows from the table specified in the FROM clause and only the rows that match in the JOINING table.
RIGHT OUTER JOIN this gets all the rows from the table specified in the JOIN clause and only the rows that match in the FROM clause.
FULL OUTER JOIN this will get all the rows from both tables.
SELF JOIN this is used when you need to join the table back to its self to return data.
I have a select SQL query which is really big and it should be pulling in about 5000 records. But when I use the JOIN It cuts the number of records to say 1000 because it only shows records where a value exists on the joined value, how would I go about pulling all records no matter whether the Join finds that a value exists or NOT?
Left outer join : MSDN Outer Joins
Instead of performing an inner join, perform a left outer join
So here's the scenario, I have two tables say payment and receipt with fields
payment_date, payment_amount, payment_party_code
and similarly
receipt_date, receipt_amount, receipt_party_code.
I have 4 rows in payment table, and 11 rows in receipt table.
What I want to do is select all rows from payment as well as from receipt table where the party_code is same. I did by using left outer join but failed because it is doing cartesian product of data.
Please help me out with this
Thanks
If you want ONLY the records that match on the payment_party_code, you should use an "INNER JOIN". But as marc_s said, you need to make sure that you specify your join criteria in your "ON" clause.
You need to use a LEFT OUTER JOIN and define a JOIN condition on it:
SELECT
p.payment_date, p.payment_amount, p.payment_party_code,
r.receipt_date, r.receipt_amount, r.receipt_party_code
FROM
dbo.Payment p
LEFT OUTER JOIN
dbo.Receipt r ON p.payment_party_code = r.receipt_party_code
This is for SQL Server (T-SQL). If you leave out the JOIN condition (the ON p.payment_party_code = r.receipt_party_code part), you'll get a cartesian product.
This will list all rows from the Payment table, and if they have info in the Receipt table, that'll be displayed as well.
If you want the opposite (everything from Receipt, even if there's no corresponding row in Payment for it), you need to either switch around the tables in the FROM ... LEFT OUTER JOIN (select from Receipt first), or you need to use a RIGHT OUTER JOIN so that you'll get everything from Receipt.
You might want to look at the Venn diagrams of SQL JOINs posted by Jeff Atwood - makes it quite clear what the different JOIN types really do...
Left Outer Join
The Left Outer Join logical operator returns each row that satisfies the join of the first (top) input with the second (bottom) input. It also returns any rows from the first input that had no matching rows in the second input. The nonmatching rows in the second input are returned as null values. If no join predicate exists in the Argument column, each row is a matching row
SELECT
pay.payment_date, pay.payment_amount, pay.payment_party_code,
rec.receipt_date, rec.receipt_amount, rec.receipt_party_code
FROM
payment pay
LEFT OUTER JOIN
receipt rec ON pay.payment_party_code = rec.receipt_party_code
select *
from party p
left outer join receipt r on p.party_code = r.party_code
Question about SQL View. Trying to develop a view from two tables. The two tables have same Primary Keys, execpt the 1st table has all of them, the 2nd has some, but not all. When I INNER Join them, I get a recordset but its not complete, because the 2nd table doesnt have all the records in it. Is there a way in my view to write logic stating that if the key isnt in there int he table #2 to insert a zero so the entire record set is shown in the view? I wan tto show ALL the records in the view even if theres nothing to inner join.
My example below:
SELECT dbo.Baan_view1b.Number, dbo.Baan_view1b.description, dbo.Baan_view1b.system, dbo.Baan_view1b.Analyst, dbo.Baan_view1b.[User],
dbo.Baan_view1b.[Date Submitted], dbo.Baan_view1b.category, dbo.Baan_view1b.stage, MAX(dbo.notes.percent_developed) AS Expr1
FROM dbo.Baan_view1b INNER JOIN
dbo.notes ON dbo.Baan_view1b.Number = dbo.notes.note_number
GROUP BY dbo.Baan_view1b.Number, dbo.Baan_view1b.description, dbo.Baan_view1b.system, dbo.Baan_view1b.Analyst, dbo.Baan_view1b.[User],
dbo.Baan_view1b.[Date Submitted], dbo.Baan_view1b.category, dbo.Baan_view1b.stage
HAVING (NOT (dbo.Baan_view1b.stage LIKE 'Closed'))
what you are looking for is the Left Join (left outer join) and not the inner join
SELECT dbo.Baan_view1b.Number, dbo.Baan_view1b.description, dbo.Baan_view1b.system, dbo.Baan_view1b.Analyst,
dbo.Baan_view1b.[User], dbo.Baan_view1b.[Date Submitted], dbo.Baan_view1b.category, dbo.Baan_view1b.stage,
MAX(dbo.notes.percent_developed) AS Expr1
FROM dbo.Baan_view1b
LEFT OUTER JOIN dbo.notes
ON dbo.Baan_view1b.Number = dbo.notes.note_number
WHERE NOT dbo.Baan_view1b.stage LIKE 'Closed'
GROUP BY dbo.Baan_view1b.Number, dbo.Baan_view1b.description, dbo.Baan_view1b.system, dbo.Baan_view1b.Analyst,
dbo.Baan_view1b.[User], dbo.Baan_view1b.[Date Submitted], dbo.Baan_view1b.category, dbo.Baan_view1b.stage
Also, changing the HAVING Clause to a WHERE clause makes the query more efficient.
Yes, you can do this. Assuming that baan_view1b has all the records and notes has only some, change
FROM dbo.Baan_view1b INNER JOIN dbo.notes
to say
FROM dbo.Baan_view1b LEFT OUTER JOIN dbo.notes
INNER JOIN (or just plain JOIN) tells the database engine to take records from Baan_view1b, match them up with records in notes, and include a row in the output for every pair of records that match. As you have seen, it excludes records from Baan_view1b that don't have matches in the notes table.
LEFT OUTER JOIN instead tells the engine to take ALL the records from Bann_view1b (because it's on the left side of the JOIN keywords). Then, it will match up records from notes wherever it can. However, you are guaranteed a row in the output for every row in the left-hand table regardless of whether it can be matched.
If, as is usual, you asked for column values from both tables, the columns from the table on the right-hand side of the JOIN will have NULL values in the missing rows.
Change the inner join to a left outer join.
(Or a right outer join or a full outer join if you feel fancy.)
You need a outer join. This shows all records that have a matching key as well as the ones that don't. The inner join only shows records that have matching join keys.
Enjoy!
You need to do a Left Outer Join as other posters have already mentioned. More information can be found here.