IS NULL left outer join?
LEFT OUTER JOIN returns every record in the left table and all matching records from the right table. If there’s no match found, a NULL is shown next to the unmatched record. RIGHT OUTER JOIN returns every record in the right table and all matching records from the left table.
Do joins work on nulls?
As we have seen from the above examples joining NULL values does not work. Even though you have two NULL values SQL Server does not treat these as the same value. Internally a value of NULL is an unknown value and therefore SQL Server does not equate an unknown value being equal to another unknown value.
Which join does not contain NULL?
A join that displays only the rows that have a match in both joined tables. Columns containing NULL do not match any values when you are creating an inner join and are therefore excluded from the result set. Null values do not match other null values.
Where Not Exists vs left outer join?
EXISTS and NOT EXISTS both short circuit – as soon as a record matches the criteria it’s either included or filtered out and the optimizer moves on to the next record. LEFT JOIN will join ALL RECORDS regardless of whether they match or not, then filter out all non-matching records.
Why left outer join is used?
A left outer join is a method of combining tables. The result includes unmatched rows from only the table that is specified before the LEFT OUTER JOIN clause. If you are joining two tables and want the result set to include unmatched rows from only one table, use a LEFT OUTER JOIN clause or a RIGHT OUTER JOIN clause.
How are NULLs treated in joins?
Null values in tables or views being joined never match each other. Since bit columns do not permit null values, a value of 0 appears in an outer join when there is no match for a bit column in the inner table. The result of a join of null with any other value is null.
Which join includes NULLs?
In SQL Full Outer Join, all rows from both the tables are included. If there are any unmatched rows, it shows NULL values for them.
Does NULL join with NULL?
The result of a join of null with any other value is null. Because null values represent unknown or inapplicable values, Transact-SQL has no basis to match one unknown value to another. You can detect the presence of null values in a column from one of the tables being joined only by using an outer join.
When to use LEFT OUTER JOIN vs not exists?
If I want to find a set of entries in table A but not in table B, I can use either LEFT OUTER JOIN or NOT EXISTS. I’ve heard SQL Server is geared towards ANSI and in some case LEFT OUTER JOINs are far more efficient than NOT EXISTS.
Is left join/is null faster than not exists or not in?
In my case, using LEFT JOIN/IS NULL returned 5 times faster than using NOT EXISTS or NOT IN, having 20000 and 4000 rows in the table1 and table2 respectively. The join was on not null columns for selecting all the rows in table1 not in table2. I realize this is an old post, but hopefully the author is still reading it. Very interesting data.
Why is MY SQL Server left join/is null not working?
SQL Server ‘s optimizer cannot discern an ANTI JOIN in a LEFT JOIN / IS NULL construct. That’s why it just build the complete resultset (as with a common LEFT JOIN) and filters out the matching values. Since we have lots of values to filter in this case (almost 10,000,000 ), it’s a hard job to filter such a tremendous lot of values.
Are not in and not exists the same?
It will depend on the data and tables. In the case of OUTER JOIN and NOT EXISTS they are the same. However to your opening sentence, NOT IN and NOT EXISTS are not the same if NULL is accepted on model.