What is the difference between LEFT JOIN
and LEFT OUTER JOIN
?
This question is related to
sql-server
tsql
left-join
outer-join
What is the difference between left join and left outer join?
Nothing. LEFT JOIN
and LEFT OUTER JOIN
are equivalent.
I find it easier to think of Joins in the following order:
Until I figured out this (relatively) simple model, JOINS were always a bit more of a black art. Now they make perfect sense.
Hope this helps more than it confuses.
C) Outer join:
There are three type of outer join
1) Left Outer Join = Left Join
2) Right Outer Join = Right Join
3) Full Outer Join = Full Join
Hope it'd help.
What is the difference between left join and left outer join?
Nothing. LEFT JOIN
and LEFT OUTER JOIN
are equivalent.
Why are LEFT/RIGHT and LEFT OUTER/RIGHT OUTER the same? Let's explain why this vocabulary. Understand that LEFT and RIGHT joins are specific cases of the OUTER join, and therefore couldn't be anything else than OUTER LEFT/OUTER RIGHT. The OUTER join is also called FULL OUTER as opposed to LEFT and RIGHT joins that are PARTIAL results of the OUTER join. Indeed:
Table A | Table B Table A | Table B Table A | Table B Table A | Table B
1 | 5 1 | 1 1 | 1 1 | 1
2 | 1 2 | 2 2 | 2 2 | 2
3 | 6 3 | null 3 | null - | -
4 | 2 4 | null 4 | null - | -
null | 5 - | - null | 5
null | 6 - | - null | 6
OUTER JOIN (FULL) LEFT OUTER (partial) RIGHT OUTER (partial)
It is now clear why those operations have aliases, as well as it is clear only 3 cases exist: INNER, OUTER, CROSS. With two sub-cases for the OUTER. The vocabulary, the way teachers explain this, as well as some answers above, often make it looks like there are lots of different types of join. But it's actually very simple.
C) Outer join:
There are three type of outer join
1) Left Outer Join = Left Join
2) Right Outer Join = Right Join
3) Full Outer Join = Full Join
Hope it'd help.
Left Join
and Left Outer Join
are one and the same. The former is the shorthand for the latter. The same can be said about the Right Join
and Right Outer Join
relationship. The demonstration will illustrate the equality. Working examples of each query have been provided via SQL Fiddle. This tool will allow for hands on manipulation of the query.
Given
Results
Right Join and Right Outer Join
Results
There are mainly three types of JOIN
Outer: are of three types
Cross Join: joins everything to everything
Why are LEFT/RIGHT and LEFT OUTER/RIGHT OUTER the same? Let's explain why this vocabulary. Understand that LEFT and RIGHT joins are specific cases of the OUTER join, and therefore couldn't be anything else than OUTER LEFT/OUTER RIGHT. The OUTER join is also called FULL OUTER as opposed to LEFT and RIGHT joins that are PARTIAL results of the OUTER join. Indeed:
Table A | Table B Table A | Table B Table A | Table B Table A | Table B
1 | 5 1 | 1 1 | 1 1 | 1
2 | 1 2 | 2 2 | 2 2 | 2
3 | 6 3 | null 3 | null - | -
4 | 2 4 | null 4 | null - | -
null | 5 - | - null | 5
null | 6 - | - null | 6
OUTER JOIN (FULL) LEFT OUTER (partial) RIGHT OUTER (partial)
It is now clear why those operations have aliases, as well as it is clear only 3 cases exist: INNER, OUTER, CROSS. With two sub-cases for the OUTER. The vocabulary, the way teachers explain this, as well as some answers above, often make it looks like there are lots of different types of join. But it's actually very simple.
Just in the context of this question, I want to post the 2 'APPLY' operators as well:
JOINS:
INNER JOIN = JOIN
OUTER JOIN
LEFT OUTER JOIN = LEFT JOIN
RIGHT OUTER JOIN = RIGHT JOIN
FULL OUTER JOIN = FULL JOIN
CROSS JOIN
SELF-JOIN: This is not exactly a separate type of join. This is basically joining a table to itself using one of the above joins. But I felt it is worth mentioning in the context JOIN discussions as you will hear this term from many in the SQL Developer community.
APPLY:
https://www.mssqltips.com/sqlservertip/1958/sql-server-cross-apply-and-outer-apply/
https://sqlhints.com/2016/10/23/outer-apply-in-sql-server/
Real life example, when to use OUTER / CROSS APPLY in SQL
I find APPLY operator very beneficial as they give better performance than having to do the same computation in a subquery. They are also replacement of many Analytical functions in older versions of SQL Server. That is why I believe that after being comfortable with JOINS, one SQL developer should try to learn the APPLY operators next.
Syntactic sugar, makes it more obvious to the casual reader that the join isn't an inner one.
To answer your question there is no difference between LEFT JOIN and LEFT OUTER JOIN, they are exactly same that said...
INNER JOIN - fetches data if present in both the tables.
OUTER JOIN are of 3 types:
LEFT OUTER JOIN
- fetches data if present in the left table.RIGHT OUTER JOIN
- fetches data if present in the right table.FULL OUTER JOIN
- fetches data if present in either of the two tables.CROSS JOIN, as the name suggests, does [n X m]
that joins everything to everything.
Similar to scenario where we simply lists the tables for joining (in the FROM
clause of the SELECT
statement), using commas to separate them.
Points to be noted:
JOIN
then by default it is a INNER JOIN
.OUTER
join has to be LEFT
| RIGHT
| FULL
you can not simply say OUTER JOIN
.OUTER
keyword and just say LEFT JOIN
or RIGHT JOIN
or FULL JOIN
.For those who want to visualise these in a better way, please go to this link: A Visual Explanation of SQL Joins
I'm a PostgreSQL DBA, as far as I could understand the difference between outer or not outer joins difference is a topic that has considerable discussion all around the internet. Until today I never saw a difference between those two; So I went further and I try to find the difference between those. At the end I read the whole documentation about it and I found the answer for this,
So if you look on documentation (at least in PostgreSQL) you can find this phrase:
In another words,
LEFT JOIN
and LEFT OUTER JOIN
ARE THE SAME
RIGHT JOIN
and RIGHT OUTER JOIN
ARE THE SAME
I hope it can be a contribute for those who are still trying to find the answer.
I find it easier to think of Joins in the following order:
Until I figured out this (relatively) simple model, JOINS were always a bit more of a black art. Now they make perfect sense.
Hope this helps more than it confuses.
To answer your question
In Sql Server joins syntax OUTER is optional
It is mentioned in msdn article : https://msdn.microsoft.com/en-us/library/ms177634(v=sql.130).aspx
So following list shows join equivalent syntaxes with and without OUTER
LEFT OUTER JOIN => LEFT JOIN
RIGHT OUTER JOIN => RIGHT JOIN
FULL OUTER JOIN => FULL JOIN
Other equivalent syntaxes
INNER JOIN => JOIN
CROSS JOIN => ,
Strongly Recommend Dotnet Mob Artice : Joins in Sql Server
I'm a PostgreSQL DBA, as far as I could understand the difference between outer or not outer joins difference is a topic that has considerable discussion all around the internet. Until today I never saw a difference between those two; So I went further and I try to find the difference between those. At the end I read the whole documentation about it and I found the answer for this,
So if you look on documentation (at least in PostgreSQL) you can find this phrase:
In another words,
LEFT JOIN
and LEFT OUTER JOIN
ARE THE SAME
RIGHT JOIN
and RIGHT OUTER JOIN
ARE THE SAME
I hope it can be a contribute for those who are still trying to find the answer.
To answer your question there is no difference between LEFT JOIN and LEFT OUTER JOIN, they are exactly same that said...
INNER JOIN - fetches data if present in both the tables.
OUTER JOIN are of 3 types:
LEFT OUTER JOIN
- fetches data if present in the left table.RIGHT OUTER JOIN
- fetches data if present in the right table.FULL OUTER JOIN
- fetches data if present in either of the two tables.CROSS JOIN, as the name suggests, does [n X m]
that joins everything to everything.
Similar to scenario where we simply lists the tables for joining (in the FROM
clause of the SELECT
statement), using commas to separate them.
Points to be noted:
JOIN
then by default it is a INNER JOIN
.OUTER
join has to be LEFT
| RIGHT
| FULL
you can not simply say OUTER JOIN
.OUTER
keyword and just say LEFT JOIN
or RIGHT JOIN
or FULL JOIN
.For those who want to visualise these in a better way, please go to this link: A Visual Explanation of SQL Joins
To answer your question
In Sql Server joins syntax OUTER is optional
It is mentioned in msdn article : https://msdn.microsoft.com/en-us/library/ms177634(v=sql.130).aspx
So following list shows join equivalent syntaxes with and without OUTER
LEFT OUTER JOIN => LEFT JOIN
RIGHT OUTER JOIN => RIGHT JOIN
FULL OUTER JOIN => FULL JOIN
Other equivalent syntaxes
INNER JOIN => JOIN
CROSS JOIN => ,
Strongly Recommend Dotnet Mob Artice : Joins in Sql Server
Left Join
and Left Outer Join
are one and the same. The former is the shorthand for the latter. The same can be said about the Right Join
and Right Outer Join
relationship. The demonstration will illustrate the equality. Working examples of each query have been provided via SQL Fiddle. This tool will allow for hands on manipulation of the query.
Given
Results
Right Join and Right Outer Join
Results
Syntactic sugar, makes it more obvious to the casual reader that the join isn't an inner one.
What is the difference between left join and left outer join?
Nothing. LEFT JOIN
and LEFT OUTER JOIN
are equivalent.
Just in the context of this question, I want to post the 2 'APPLY' operators as well:
JOINS:
INNER JOIN = JOIN
OUTER JOIN
LEFT OUTER JOIN = LEFT JOIN
RIGHT OUTER JOIN = RIGHT JOIN
FULL OUTER JOIN = FULL JOIN
CROSS JOIN
SELF-JOIN: This is not exactly a separate type of join. This is basically joining a table to itself using one of the above joins. But I felt it is worth mentioning in the context JOIN discussions as you will hear this term from many in the SQL Developer community.
APPLY:
https://www.mssqltips.com/sqlservertip/1958/sql-server-cross-apply-and-outer-apply/
https://sqlhints.com/2016/10/23/outer-apply-in-sql-server/
Real life example, when to use OUTER / CROSS APPLY in SQL
I find APPLY operator very beneficial as they give better performance than having to do the same computation in a subquery. They are also replacement of many Analytical functions in older versions of SQL Server. That is why I believe that after being comfortable with JOINS, one SQL developer should try to learn the APPLY operators next.
Source: Stackoverflow.com