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Visual representation of SQL joins - How SQL joining work - MySQL - MSSQL - INNER|OUTER|LEFT|RIGHT|EXCLUDING JOINS

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Visual representation of SQL joins - How SQL joining work

Note: We aggregated the following data from this page: http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins. Thank you very much C.L. Moffatt for your incredible good work!

Download the Visual SQL Join overview sheet here

Inner JOIN

This is the simplest, most understood Join and is the most common. This query will return all of the records in the left table (table A) that have a matching record in the right table (table B). This Join is written as follows:

SELECT <select_list>
FROM Table_A A
INNER JOIN Table_B B
ON A.Key = B.Key

Left JOIN

This query will return all of the records in the left table (table A) regardless if any of those records have a match in the right table (table B). It will also return any matching records from the right table. This Join is written as follows:

SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key

Right JOIN

This query will return all of the records in the right table (table B) regardless if any of those records have a match in the left table (table A). It will also return any matching records from the left table. This Join is written as follows:

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key

Outer JOIN

This Join can also be referred to as a FULL OUTER JOIN or a FULL JOIN. This query will return all of the records from both tables, joining records from the left table (table A) that match records from the right table (table B). This Join is written as follows:

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key

Left Excluding JOIN

This query will return all of the records in the left table (table A) that do not match any records in the right table (table B). This Join is written as follows:

SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL

Right Excluding JOIN

This query will return all of the records in the right table (table B) that do not match any records in the left table (table A). This Join is written as follows:

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL

Outer Excluding JOIN

This query will return all of the records in the left table (table A) and all of the records in the right table (table B) that do not match. I have yet to have a need for using this type of Join, but all of the others, I use quite frequently. This Join is written as follows:

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL OR B.Key IS NULL

Examples

Suppose we have two tables, Table_A and Table_B. The data in these tables are shown below:

TABLE_A
  PK Value
---- ----------
   1 FOX
   2 COP
   3 TAXI
   6 WASHINGTON
   7 DELL
   5 ARIZONA
   4 LINCOLN
  10 LUCENT

TABLE_B
  PK Value
---- ----------
   1 TROT
   2 CAR
   3 CAB
   6 MONUMENT
   7 PC
   8 MICROSOFT
   9 APPLE
  11 SCOTCH

The results of the seven Joins are shown below:

-- INNER JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
       B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
INNER JOIN Table_B B
ON A.PK = B.PK

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
   1 FOX        TROT          1
   2 COP        CAR           2
   3 TAXI       CAB           3
   6 WASHINGTON MONUMENT      6
   7 DELL       PC            7

(5 row(s) affected)

-- LEFT JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
LEFT JOIN Table_B B
ON A.PK = B.PK

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
   1 FOX        TROT          1
   2 COP        CAR           2
   3 TAXI       CAB           3
   4 LINCOLN    NULL       NULL
   5 ARIZONA    NULL       NULL
   6 WASHINGTON MONUMENT      6
   7 DELL       PC            7
  10 LUCENT     NULL       NULL

(8 row(s) affected)

-- RIGHT JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
RIGHT JOIN Table_B B
ON A.PK = B.PK

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
   1 FOX        TROT          1
   2 COP        CAR           2
   3 TAXI       CAB           3
   6 WASHINGTON MONUMENT      6
   7 DELL       PC            7
NULL NULL       MICROSOFT     8
NULL NULL       APPLE         9
NULL NULL       SCOTCH       11

(8 row(s) affected)

-- OUTER JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.PK = B.PK

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
   1 FOX        TROT          1
   2 COP        CAR           2
   3 TAXI       CAB           3
   6 WASHINGTON MONUMENT      6
   7 DELL       PC            7
NULL NULL       MICROSOFT     8
NULL NULL       APPLE         9
NULL NULL       SCOTCH       11
   5 ARIZONA    NULL       NULL
   4 LINCOLN    NULL       NULL
  10 LUCENT     NULL       NULL

(11 row(s) affected)

-- LEFT EXCLUDING JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
LEFT JOIN Table_B B
ON A.PK = B.PK
WHERE B.PK IS NULL

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
   4 LINCOLN    NULL       NULL
   5 ARIZONA    NULL       NULL
  10 LUCENT     NULL       NULL
(3 row(s) affected)

-- RIGHT EXCLUDING JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
RIGHT JOIN Table_B B
ON A.PK = B.PK
WHERE A.PK IS NULL

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
NULL NULL       MICROSOFT     8
NULL NULL       APPLE         9
NULL NULL       SCOTCH       11

(3 row(s) affected)

-- OUTER EXCLUDING JOIN
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.PK = B.PK
WHERE A.PK IS NULL
OR B.PK IS NULL

A_PK A_Value    B_Value    B_PK
---- ---------- ---------- ----
NULL NULL       MICROSOFT     8
NULL NULL       APPLE         9
NULL NULL       SCOTCH       11
   5 ARIZONA    NULL       NULL
   4 LINCOLN    NULL       NULL
  10 LUCENT     NULL       NULL

(6 row(s) affected)