LEFT JOIN vs LEFT OUTER JOIN in SQL Server

Question

What is the difference between LEFT JOIN and LEFT OUTER JOIN

User · Answer

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    The words INNER and OUTER are optional in all forms  INNER is the default  LEFT  RIGHT  and FULL imply an outer join     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

User · Answer

As per the documentation  FROM  Transact-SQL     lt join type gt               INNER       LEFT   RIGHT   FULL     OUTER          lt join hint gt          JOIN   The keyword OUTER is marked as optional  enclosed in square brackets   In this specific case  whether you specify OUTER or not makes no difference   Note that while the other elements of the join clause is also marked as optional  leaving them out will make a difference   For instance  the entire type-part of the JOIN clause is optional  in which case the default is INNER if you just specify JOIN  In other words  this is legal   SELECT   FROM A JOIN B ON A X   B Y   Here s a list of equivalent syntaxes   A LEFT JOIN B            A LEFT OUTER JOIN B A RIGHT JOIN B           A RIGHT OUTER JOIN B A FULL JOIN B            A FULL OUTER JOIN B A INNER JOIN B           A JOIN B   Also take a look at the answer I left on this other SO question  SQL left join vs multiple tables on FROM line

User · Answer

There are mainly three types of JOIN   Inner  fetches data  that are present in both tables  Only JOIN means INNER JOIN  Outer  are of three types   LEFT OUTER - - fetches data present only in left table  amp  matching condition RIGHT OUTER - - fetches data present only in right table  amp  matching condition FULL OUTER - - fetches data present any or both table  LEFT or RIGHT or FULL  OUTER JOIN can be written w o writing  OUTER   Cross Join  joins everything to everything

User · Answer

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    CROSS APPLY  -- Similar to INNER JOIN  But has added advantage of being able to compute something in the Right table for each row of the Left table and would return only the matching rows  OUTER APPLY  -- Similar to LEFT OUTER JOIN  But has added advantage of being able to compute something in the Right table for each row of the Left table and would return all the rows from the Left table irrespective of a match on the Right table    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

User · Answer

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    The words INNER and OUTER are optional in all forms  INNER is the default  LEFT  RIGHT  and FULL imply an outer join     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

User · Answer

Syntactic sugar  makes it more obvious to the casual reader that the join isn t an inner one

User · Answer

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    Left Join and Left Outer Join    Results      Right Join and Right Outer Join    Results

User · Answer

As per the documentation  FROM  Transact-SQL     lt join type gt               INNER       LEFT   RIGHT   FULL     OUTER          lt join hint gt          JOIN   The keyword OUTER is marked as optional  enclosed in square brackets   In this specific case  whether you specify OUTER or not makes no difference   Note that while the other elements of the join clause is also marked as optional  leaving them out will make a difference   For instance  the entire type-part of the JOIN clause is optional  in which case the default is INNER if you just specify JOIN  In other words  this is legal   SELECT   FROM A JOIN B ON A X   B Y   Here s a list of equivalent syntaxes   A LEFT JOIN B            A LEFT OUTER JOIN B A RIGHT JOIN B           A RIGHT OUTER JOIN B A FULL JOIN B            A FULL OUTER JOIN B A INNER JOIN B           A JOIN B   Also take a look at the answer I left on this other SO question  SQL left join vs multiple tables on FROM line

User · Answer

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

User · Answer

What is the difference between left join and left outer join    Nothing  LEFT JOIN and LEFT OUTER JOIN are equivalent

User · Answer

There are mainly three types of JOIN   Inner  fetches data  that are present in both tables  Only JOIN means INNER JOIN  Outer  are of three types   LEFT OUTER - - fetches data present only in left table  amp  matching condition RIGHT OUTER - - fetches data present only in right table  amp  matching condition FULL OUTER - - fetches data present any or both table  LEFT or RIGHT or FULL  OUTER JOIN can be written w o writing  OUTER   Cross Join  joins everything to everything

User · Answer

What is the difference between left join and left outer join    Nothing  LEFT JOIN and LEFT OUTER JOIN are equivalent

User · Answer

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    Left Join and Left Outer Join    Results      Right Join and Right Outer Join    Results

User · Answer

To answer your question there is no difference between LEFT JOIN   and LEFT OUTER JOIN  they are exactly same that said      At the top level there are mainly 3 types of joins    INNER OUTER CROSS      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    If you just mention JOIN then by default it is a INNER JOIN  An OUTER join has to be LEFT   RIGHT   FULL you can not simply say OUTER JOIN  You can drop 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

User · Answer

As per the documentation  FROM  Transact-SQL     lt join type gt               INNER       LEFT   RIGHT   FULL     OUTER          lt join hint gt          JOIN   The keyword OUTER is marked as optional  enclosed in square brackets   In this specific case  whether you specify OUTER or not makes no difference   Note that while the other elements of the join clause is also marked as optional  leaving them out will make a difference   For instance  the entire type-part of the JOIN clause is optional  in which case the default is INNER if you just specify JOIN  In other words  this is legal   SELECT   FROM A JOIN B ON A X   B Y   Here s a list of equivalent syntaxes   A LEFT JOIN B            A LEFT OUTER JOIN B A RIGHT JOIN B           A RIGHT OUTER JOIN B A FULL JOIN B            A FULL OUTER JOIN B A INNER JOIN B           A JOIN B   Also take a look at the answer I left on this other SO question  SQL left join vs multiple tables on FROM line

User · Answer

Syntactic sugar  makes it more obvious to the casual reader that the join isn t an inner one

User · Answer

To answer your question there is no difference between LEFT JOIN   and LEFT OUTER JOIN  they are exactly same that said      At the top level there are mainly 3 types of joins    INNER OUTER CROSS      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    If you just mention JOIN then by default it is a INNER JOIN  An OUTER join has to be LEFT   RIGHT   FULL you can not simply say OUTER JOIN  You can drop 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

User · Answer

As per the documentation  FROM  Transact-SQL     lt join type gt               INNER       LEFT   RIGHT   FULL     OUTER          lt join hint gt          JOIN   The keyword OUTER is marked as optional  enclosed in square brackets   In this specific case  whether you specify OUTER or not makes no difference   Note that while the other elements of the join clause is also marked as optional  leaving them out will make a difference   For instance  the entire type-part of the JOIN clause is optional  in which case the default is INNER if you just specify JOIN  In other words  this is legal   SELECT   FROM A JOIN B ON A X   B Y   Here s a list of equivalent syntaxes   A LEFT JOIN B            A LEFT OUTER JOIN B A RIGHT JOIN B           A RIGHT OUTER JOIN B A FULL JOIN B            A FULL OUTER JOIN B A INNER JOIN B           A JOIN B   Also take a look at the answer I left on this other SO question  SQL left join vs multiple tables on FROM line

User · Answer

Syntactic sugar  makes it more obvious to the casual reader that the join isn t an inner one

User · Answer

There are only 3 joins    A  Cross Join    Cartesian          E g  Table A  Table B    B  Inner Join      JOIN             E g  Table A Join Inner Join Table B  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

User · Answer

What is the difference between left join and left outer join    Nothing  LEFT JOIN and LEFT OUTER JOIN are equivalent

User · Answer

I find it easier to think of Joins in the following order    CROSS JOIN - a Cartesian product of both tables   ALL joins begin here INNER JOIN - a CROSS JOIN with a filter added   OUTER JOIN - an INNER JOIN with missing elements  from either LEFT or RIGHT table  added afterward    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

User · Answer

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   gt  LEFT JOIN RIGHT OUTER JOIN   gt  RIGHT JOIN FULL OUTER JOIN   gt  FULL JOIN   Other equivalent syntaxes  INNER JOIN   gt  JOIN CROSS JOIN   gt      Strongly Recommend Dotnet Mob Artice   Joins in Sql Server

User · Answer

What is the difference between left join and left outer join    Nothing  LEFT JOIN and LEFT OUTER JOIN are equivalent

User · Answer

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    CROSS APPLY  -- Similar to INNER JOIN  But has added advantage of being able to compute something in the Right table for each row of the Left table and would return only the matching rows  OUTER APPLY  -- Similar to LEFT OUTER JOIN  But has added advantage of being able to compute something in the Right table for each row of the Left table and would return all the rows from the Left table irrespective of a match on the Right table    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

User · Answer

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

User · Answer

Syntactic sugar  makes it more obvious to the casual reader that the join isn t an inner one

User · Answer

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   gt  LEFT JOIN RIGHT OUTER JOIN   gt  RIGHT JOIN FULL OUTER JOIN   gt  FULL JOIN   Other equivalent syntaxes  INNER JOIN   gt  JOIN CROSS JOIN   gt      Strongly Recommend Dotnet Mob Artice   Joins in Sql Server

User · Answer

I find it easier to think of Joins in the following order    CROSS JOIN - a Cartesian product of both tables   ALL joins begin here INNER JOIN - a CROSS JOIN with a filter added   OUTER JOIN - an INNER JOIN with missing elements  from either LEFT or RIGHT table  added afterward    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

User · Answer

There are only 3 joins    A  Cross Join    Cartesian          E g  Table A  Table B    B  Inner Join      JOIN             E g  Table A Join Inner Join Table B  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

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