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
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
This question already has answers here:
What is the difference between "INNER JOIN" and "OUTER JOIN"?
(28 answers)
Closed 8 years ago.
I have about 6 months novice experience in SQL, TSQL, SSIS, ETL. As I find myself using JOIN statements more and more in my intern project I have been experimenting with the different JOIN statements. I wanted to confirm my findings. Are the following statements accurate pertaining to the conclusion of JOIN statements in SQL Server?:
1)I did a LEFT OUTER JOIN query and did the same query using JOIN which yielded the same results; are all JOIN statements LEFT OUTER associated in SQL Server?
2)I did a LEFT OUTER JOIN WHERE 2nd table PK (joined to) IS NOT NULL and did the same query using an INNER JOIN which yielded the same results; is it safe to say the the INNER JOIN statement will yield only matched records? and is the same as LEFT OUTER JOIN where joined records IS NOT NULL ?
The reason I'm asking is because I have been only using LEFT OUTER JOINS because that is what I was comfortable with. However, I want to eliminate as much code as possible when writing queries to be more efficient. I just wanted to make sure my observations are correct.
Also, are there any tips that you could provide on easily figuring out which JOIN statement is appropriate for specific queries? For instance, what JOIN would you use if you wanted to yield non-matching records?
Thanks.
A join or inner join (same thing) between table A and table B on, for instance, field1, would narrow in on all rows of table A and B sharing the same field1 value.
A left outer join between A and B, on field1, would show all rows of table A, and only those rows of table B that have a field1 existing in table A.
Where the rows of field1 on table A have a field1 value that doesn't exist in table B, the table B value would show null for field1, but the row of table A would be retained because it is an outer join. These are rows that wouldn't show up in a join which is an implied inner join.
If you get the same results doing a join between table A and table B as you do a left outer join between table A and B, then whatever fields you're joining on have values that exist in both tables. No value for any of the joined fields in A or B exist exclusively in A or B, they all exist in both A and B.
It is also possible you're putting criteria into the where clause that belongs in the on clause of the outer join, which may be causing your confusion. In my example above of tables A and B, where A is being left outer joined with B, you would put any criteria related to table B in the on clause, not the where clause, otherwise you would essentially be turning the outer join into an inner join. For example if you had b.field4 = 12 in the WHERE clause, and table B didn't have a match with A, it would be null and that criteria would fail, and it'd no longer come back even though you used a left outer join. That may be what you are referring to.
JOIN's are mapped to 'INNER JOIN' by default
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.
Actually if i am doing INNER JOIN of two tables then i will get all matched records from the two tables.
But i want to get all the unmatched rows only.
Is there any way to do that?
Or Any JOIN available for that?
There is join you can use. You need an OUTER JOIN, and only select rows with a NULL on the join condition.
Another option is to use a sub query with a NOT EXISTS or NOT IN as part of your main WHERE clause.
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