Sql Joins Query

Joins

1. Inner Join 2. Outer Join

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Left Outer Join

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Right Outer Join

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Full Outer Join

3. Cross Join

Joins in SQL Server allows the retrieval of data records from one or more tables having some relation between them. Logical operators can also be used to drill down the number of records to get the desired output from sql join queries.

Inner Join: Inner Join is a default type join of SQL Server. It uses logical operators such as =, <, > to match the records in two tables. Inner Join includes equi join and natural joins. Examples: SQL Inner Join Examples Equi Join: Equi Join returns all the columns from both tables and filters the records satisfying the matching condition specified in Join “ON” statement of sql inner join query. SQL Inner Equi Join Example: USE NORTHWIND SELECT * FROM CATEGORIES C INNER JOIN PRODUCTS P ON P.CATEGORYID = C.CATEGORYID

Result will display the following columns: CategoryID, CategoryName, Description, Picture, ProductID, ProductName, SupplierID, CategoryID, QuantityPerUnit, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued Above equi join sql query will display the categoryId two times in a row because both the tables have categoryId column. You can convert the result into natural join by elimination the identical columns and unnecessary columns. In the previous article you learnt how to use equi inner join in sql queries to join two tables and retrieve the combined result of both sql database tables. See the example of equi join here… SQL Inner Equi Join Examples. Notice that equi join sql query returned the categoryId column twice because of relation between two tables. Products table also has categoryId column that shows the product belongs to a particular category in categories whose categoryId is also saved in products table as a relational key between both the tables.

Natural join query example: SELECT C.*, P.PRODUCTID, P.PRODUCTNAME FROM CATEGORIES C INNER JOIN PRODUCTS P ON P.CATEGORYID = C.CATEGORYID

This natural join query will return all the columns of categories table and prodcutId and productName from products table.

You can further modify this natural inner join query as per your requirements to visualize the data by specifying the column names of categories table also.

Inner Join Query Example by specifying column names: SELECT C.CATEGORYID, C.CATEGORYNAME, P.PRODUCTID, P.PRODUCTNAME, P.UNITPRICE FROM CATEGORIES C INNER JOIN PRODUCTS P ON P.CATEGORYID = C.CATEGORYID

This inner join query will display only the specified column names of both the tables. Equi Join (Inner Join) for combining the columns of two sql database tables into single table output result. Try sql inner equi join examples.

Natural Join (Inner Join) for getting the output of equi join into the specified columns format and removing the ambiguous column names from the output. See sql inner natural join examples.

SQL Inner Join query with (=) operator:

SELECT C.CATEGORYID, C.CATEGORYNAME, P.PRODUCTID, P.PRODUCTNAME, P.UNITPRICE FROM CATEGORIES C INNER JOIN PRODUCTS P ON P.CATEGORYID = C.CATEGORYID WHERE P.UNITPRICE = 10 ORDER BY C.CATEGORYNAME, P.PRODUCTNAME

This inner join query will return the categoryid, categoryname, productid, productname, unitprice where product unit price = 10

SQL Inner Join Query with (>) operator:

SELECT DISTINCT C.CATEGORYID, C.CATEGORYNAME FROM CATEGORIES C INNER JOIN PRODUCTS P ON C.CATEGORYID > P.CATEGORYID WHERE P.UNITPRICE = 10 ORDER BY C.CATEGORYNAME

This inner join query will return the categoryId, categoryName having products with unit price=10

SQL Inner Join Query with not equal (<>) operator:

SELECT DISTINCT P1.PRODUCTNAME, P1.UNITPRICE, P1.SUPPLIERID FROM PRODUCTS P1 INNER JOIN PRODUCTS P2 ON P1.SUPPLIERID=P2.SUPPLIERID AND P1.UNITPRICE<>P2.UNITPRICE WHERE P1.UNITPRICE < 20 AND P2.UNITPRICE < 20 ORDER BY P1.SUPPLIERID

Inner Join with not equal operator is rarely used in self joins. As an example above sql self join query returns the productname, unitprice, supplierid where suppliers having 2 or more than 2 products with unit price less than 20.

Outer Join: Outer Join has further 3 sub categories as left, right and full. Outer Join uses these category names as keywords that can be specified in the FROM clause.

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Left Outer Join: Left Outer Join returns all the rows from the table specified first in the Left Outer Join Clause. If in the left table any row has no matching record in the right side table then that row returns null column values for that particular tuple. Examples:

Inner joins return only those rows from both sql database tables having matching records in both the tables whereas left outer join returns all the rows from the left table and related matching records from the other one. SQL Left Outer Join Example: USE PUBS SELECT A.AU_FNAME, A.AU_LNAME, P.PUB_NAME FROM AUTHORS A LEFT OUTER JOIN PUBLISHERS P ON A.CITY = P.CITY ORDER BY A.AU_LNAME, A.AU_FNAME Result: au_fname

au_lname

pub_name

Abraham

Bennet

Algodata Infosystems

Reginald

BlotchetHalls

NULL

Cheryl

Carson

Algodata Infosystems

Michel

DeFrance

NULL

Innes

del Castillo

NULL

Ann

Dull

NULL

Marjorie

Green

NULL

Morningstar

Greene

NULL

Burt

Gringlesby

NULL

Sheryl

Hunter

NULL

Livia

Karsen

NULL

Charlene

Locksley

NULL

Stearns

MacFeather

NULL

Heather

McBadden

NULL

Michael

O'Leary

NULL

Sylvia

Panteley

NULL

Albert

Ringer

NULL

Anne

Ringer

NULL

Meander

Smith

NULL

Dean

Straight

NULL

Dirk

Stringer

NULL

Johnson

White

NULL

Akiko

Yokomoto

NULL

This left outer join query retrieves the author names and publisher name having same cities. Here all rows retrieved from the left table i.e. authors and publisher name having the similar city other columns of pub_name column are null due to no match found in the right table.

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Right Outer Join: Right Outer Join is exactly the reverse method of Left Outer Join. It returns all the rows from right table and returns null values for the rows having no match in the left joined table. Examples:

SQL Right Outer Join Examples In the previous article regarding sql left outer join we learnt left outer join that retrieves all the results from left table and related matches from the right table where right table having no matches displays the Null value in the corresponding columns. Consider the same example of authors and publishers table of the existing database PUBS of sql server 2000. We used the following left outer join query: SELECT A.AU_FNAME, A.AU_LNAME, P.PUB_NAME FROM AUTHORS A LEFT OUTER JOIN PUBLISHERS P ON A.CITY = P.CITY ORDER BY A.AU_LNAME, A.AU_FNAME Just change the left keyword to right outer join in above example; you will get the reverse output of left outer join in the form of right outer join. SQL Right Outer Join query Example: SELECT A.AU_FNAME, A.AU_LNAME, P.PUB_NAME FROM AUTHORS A RIGHT OUTER JOIN PUBLISHERS P ON A.CITY = P.CITY ORDER BY A.AU_LNAME, A.AU_FNAME Result: au_fname au_lname pub_name NULL

NULL

New Moon Books

NULL

NULL

Binnet & Hardley

NULL

NULL

Five Lakes Publishing

NULL

NULL

Ramona Publishers

NULL

NULL

GGG&G

NULL

NULL

Scootney Books

NULL

NULL

Lucerne Publishing

Abraham

Bennet

Algodata Infosystems

Cheryl

Carson

Algodata Infosystems

Notice the difference in the output of right outer join and left outer join. Right outer join returned all the rows from right table as all publisher names and null values for the left table columns having no match found in left table’s au_fname and au_lname.

Full Outer Join: Full outer join returns all the rows from both left and right joined tables. If there is any match missing from the left table then it returns null column values for left side table and if there is any match missing from right table then it returns null value columns for the right side table. Examples: SQL Full Outer Join Examples To retrieve all the records from left as well as right table unless the records have matching relations in each row you can use SQL FULL OUTER JOIN. You can consider the examples of last two articles about left outer join and right outer join, in

which left outer join retrieves all records from the left table and as all records of right table in right outer join along with null values for the columns having no matching records in any tuple. To retain all the records of left as well as right table along with null values for non matching rows displaying the combination of results of left outer and right outer join, FULL OUTER JOIN is the best solution. SQL FULL outer join example: SELECT A.AU_FNAME, A.AU_LNAME, P.PUB_NAME FROM AUTHORS A FULL OUTER JOIN PUBLISHERS P ON A.CITY = P.CITY ORDER BY A.AU_LNAME, A.AU_FNAME Result: au_fname au_lname

pub_name

NULL

NULL

Binnet & Hardley

NULL

NULL

Five Lakes Publishing

NULL

NULL

New Moon Books

NULL

NULL

Lucerne Publishing

NULL

NULL

Scootney Books

NULL

NULL

Ramona Publishers

NULL

NULL

GGG&G

Abraham

Bennet

Algodata Infosystems

Reginald

Blotchet-Halls NULL

Cheryl

Carson

Algodata Infosystems

Michel

DeFrance

NULL

Innes

del Castillo

NULL

Ann

Dull

NULL

Marjorie

Green

NULL

Morningstar Greene

NULL

Burt

Gringlesby

NULL

Sheryl

Hunter

NULL

Livia

Karsen

NULL

Charlene

Locksley

NULL

Stearns

MacFeather

NULL

Heather

McBadden

NULL

Michael

O'Leary

NULL

Sylvia

Panteley

NULL

Albert

Ringer

NULL

Anne

Ringer

NULL

Meander

Smith

NULL

Dean

Straight

NULL

Dirk

Stringer

NULL

Johnson

White

NULL

Akiko

Yokomoto

NULL

Above output retrieved from the sql full outer join query is the exact combination of both the left as well as right join outputs.

Cross Join: Cross join works as a Cartesian product of rows for both left and right table. It combined each row of left table with all the rows of right table. SQL Cross join returns the output result as a Cartesian product of both database tables. Let left table has 10 rows and right table has 8 rows then SQL CROSS Join will return 180 rows combining each record of left table with all records of right side table. Consider the following example of CROSS Join: USE PUBS SELECT AU_FNAME, AU_LNAME, PUB_NAME FROM AUTHORS CROSS JOIN PUBLISHERS ORDER BY AU_FNAME Above cross join will return 23 * 8 = 184 results by multiplying each row of authors table with publishers table. SQL CROSS Join with WHERE clause By just adding the where clause with Cross join sql query it turns the output result into inner join. Example: USE PUBS SELECT AU_FNAME, AU_LNAME, PUB_NAME FROM AUTHORS CROSS JOIN PUBLISHERS WHERE AUTHORS.CITY = PUBLISHERS.CITY ORDER BY AU_FNAME It will display only the matching results in both tables. Result: au_fname

au_lname

pub_name

Cheryl

Carson

Algodata Infosystems

Abraham

Bennet

Algodata Infosystems

Self Join For self join in sql you can try the following example: Create table employees: emp_id

emp_name

emp_manager_id

1

John

Null

2

Tom

1

3

Smith

1

4

Albert

2

5

David

2

6

Murphy

5

7

Petra

5

Now to get the names of managers from the above single table you can use sub queries or simply the self join. Self Join SQL Query to get the names of manager and employees: select e1.emp_name 'manager',e2.emp_name 'employee' from employees e1 join employees e2 on e1.emp_id=e2.emp_manager_id Result: manager employee John

Tom

John

Smith

Tom

Albert

Tom

David

David

Murphy

David

Petra

Understanding the Self Join Example In the above self join query, employees table is joined with itself using table aliases e1 and e2. This creates the two views of a single table. from employees e1 join employees e2 on e1.emp_id=e2.emp_manager_id Here e.emp_manager_id passes the manager id from the 2nd view to the first aliased e1 table to get the names of managers.

select * from authors select au_id,au_lname,city from authors INSERT INTO authors (au_id,au_lname,au_fname,phone,address,city,state,zip,contractpup) VALUES (005,'FirstCol', 'SecondCol','999999999','','','tn','60001',1) select * from authors where au_lname like '%First%' select * from authors where city ='oakland' and state='CA' select * from authors where city ='oakland' and state='CA' and zip='94609'

select * from authors where city ='oakland' or state='CA' or zip='94609' order by city desc SELECT state , COUNT(au_id) As total FROM authors WHERE state IN('UT', 'CA') GROUP BY state UPDATE authors SET state = 'TN',city='Chennai' WHERE zip = '60001' select * from authors where state='tn'