sql server joins

8/11/2019 SQL Server Joins

1/10

SQL SERVER Introduction to JOINsBasic of JOINs

INNER JOINThis join returns rows when there is at least one match in both the tables.


2/10

OUTER JOINThere are three different Outer Join methods.

LEFT OUTER JOIN

This join returns all the rows from the left table in conjunction with the matching rows from the right table. Ifthere are no columns matching in the right table, it returns NULL values.


3/10

RIGHT OUTER JOIN

This join returns all the rows from the right table in conjunction with the matching rows from the left table. If

there are no columns matching in the left table, it returns NULL values.


4/10

FULL OUTER JOIN

This join combines left outer join and right outer join. It returns row from either table when the conditions are

met and returns null value when there is no match.


5/10

CROSS JOIN

This join is a Cartesian join that does not necessitate any condition to join. The resultset contains records thatare multiplication of record number from both the tables.


6/10

Additional Notes related to JOIN:

The following are three classic examples to display where Outer Join is useful. You will notice severalinstances where developers write query as given below.

SELECTt1.*

FROMTable1 t1

WHEREt1.IDNOTIN(SELECTt2.IDFROMTable2 t2)GO

The query demonstrated above can be easily replaced by Outer Join. Indeed, replacing it by Outer Join is the

best practice. The query that gives same result as above is displayed here using Outer Join and WHERE clause

in join.

/* LEFT JOIN - WHERE NULL */SELECTt1.*,t2.*

FROMTable1 t1

LEFTJOINTable2 t2ONt1.ID=t2.IDWHEREt2.IDISNULL


7/10

The above example can also be created using Right Outer Join.


8/10

NOT INNER JOIN

Remember, the term Not Inner Join does not exist in database terminology. However, when full Outer Join is

used along with WHERE condition, as explained in the above two examples, it will give you exclusive result

to Inner Join. This join will give all the results that were not present in Inner Join.

USEAdventureWorksGOCREATE TABLEtable1

(IDINT,ValueVARCHAR(10))

INSERT INTOTable1(ID,Value)

SELECT1,'First'

UNIONALL

SELECT2,'Second'

UNIONALL

SELECT3,'Third'

UNIONALLSELECT4,'Fourth'

UNIONALL

SELECT5,'Fifth'GOCREATE TABLEtable2

(IDINT,ValueVARCHAR(10))

INSERT INTOTable2(ID,Value)


9/10

SELECT1,'First'

UNIONALL

SELECT2,'Second'

UNIONALL

SELECT3,'Third'

UNIONALLSELECT6,'Sixth'

UNIONALL

SELECT7,'Seventh'

UNIONALL

SELECT8,'Eighth'GOSELECT*

FROMTable1

SELECT*

FROMTable2GOUSEAdventureWorksGO/* INNER JOIN */SELECTt1.*,t2.*

FROMTable1 t1

INNER JOINTable2 t2ONt1.ID=t2.IDGO/* LEFT JOIN */SELECTt1.*,t2.*

FROMTable1 t1

LEFTJOINTable2 t2ONt1.ID=t2.IDGO/* RIGHT JOIN */SELECTt1.*,t2.*

FROMTable1 t1

RIGHTJOINTable2 t2ONt1.ID=t2.IDGO/* OUTER JOIN */SELECTt1.*,t2.*

FROMTable1 t1

FULLOUTERJOINTable2 t2ONt1.ID=t2.IDGO/* LEFT JOIN - WHERE NULL */SELECTt1.*,t2.*

FROMTable1 t1

LEFTJOINTable2 t2ONt1.ID=t2.ID

WHEREt2.IDISNULLGO/* RIGHT JOIN - WHERE NULL */SELECTt1.*,t2.*

FROMTable1 t1

RIGHTJOINTable2 t2ONt1.ID=t2.ID


10/10

WHEREt1.IDISNULLGO/* OUTER JOIN - WHERE NULL */SELECTt1.*,t2.*

FROMTable1 t1

FULLOUTERJOINTable2 t2ONt1.ID=t2.ID

WHEREt1.IDISNULL ORt2.IDISNULLGO/* CROSS JOIN */SELECTt1.*,t2.*

FROMTable1 t1

CROSSJOINTable2 t2GODROP TABLEtable1

DROP TABLEtable2GO

sql server joins

Documents