Outer Join in DBMS

January 31, 2023

About Outer Join in DBMS

In this article, we will learn about outer join in DBMS.
Outer Join between two tables helps to retrieve data that will be common to both the tables along with the unmatched data between the tables and thus helps to collect complete data from both the tables.

 

Outer Join in DBMS

Full Outer Join in DBMS

 
 

A join is a query that combines rows from two or more tables, views or materialized views

Definition: Full join returns all the matched records and unmatched records from both left side table and right side table.

A Full join is viewed as a union of an inner join, left outer join and right outer join.

 

Outer Join in DBMS
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Functional Dependencies

Joins in DBMS

Relational Algebra

Deadlock in DBMS

How full join works

  • It Returns all the records that are matched based upon the condition (inner join)
  • It Returns all the unmatched records from the right table (right outer)
  • It Returns all the unmatched record from the left table (left outer)
  • It places normal values on unmatched records when there is no data to be appended for some tuples.

Syntax:

select 
col1,col2,col3.... 
from  table1
FULL JOIN table2
on table1.common_col=table2.common_col;
Consider two tables Emp table
EMPNO ENAME JOB MGR HIRE_DATE SAL COMM DEPTNO
7839 KING PRESIDENT – 17-NOV-81 5000 – 10
7698 BLAKE MANAGER 7839 01-MAY-81 2850 – 30
7782 CLARK MANAGER 7839 09-JUN-81 2450 – 10
7566 JONES MANAGER 7839 02-APR-81 2975 – 20
7788 SCOTT ANALYST 7566 19-APR-87 3000 – 20
7902 FORD ANALYST 7566 03-DEC-81 3000 – 20
7369 SMITH CLERK 7902 17-DEC-80 800 – 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK 7788 23-MAY-87 1100 – 20
7900 JAMES CLERK 7698 03-DEC-81 950 – 30
7934 MILLER CLERK 7782 23-JAN-82 1300 – 10
Dept table
DEPTNO DNAME LOC
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON

Full Join SQL query

select rownum,Empno,Ename,Emp.Deptno,Dname, sal*12 annsal,loc,job
from 
Emp
FULL JOIN
Dept
on Emp.Deptno=Dept.deptno and dname='SALES';
O/P
ROWNUM EMPNO ENAME DEPTNO DNAME ANNUAL LOC JOB
1 7839 KING 10 – 60000 – PRESIDENT
2 7698 BLAKE 30 SALES 34200 CHICAGO MANAGER
3 7782 CLARK 10 – 29400 – MANAGER
4 7566 JONES 20 – 35700 – MANAGER
5 7788 SCOTT 20 – 36000 – ANALYST
6 7902 FORD 20 – 36000 – ANALYST
7 7369 SMITH 20 – 9600 – CLERK
8 7499 ALLEN 30 SALES 19200 CHICAGO SALESMAN
9 7521 WARD 30 SALES 15000 CHICAGO SALESMAN
10 7654 MARTIN 30 SALES 15000 CHICAGO SALESMAN
11 7844 TURNER 30 SALES 18000 CHICAGO SALESMAN
12 7876 ADAMS 20 – 13200 – CLERK
13 7900 JAMES 30 SALES 11400 CHICAGO CLERK
14 7934 MILLER 10 – 15600 – CLERK
15 – – – OPERATIONS – BOSTON –
16 – – – ACCOUNTING – NEW YORK –
17 – – – RESEARCH – DALLAS –
  • There are 6 matched records with deptno=30 and name =’SALES’ from dept table with emp table and 3 records from right side table ‘dept’ are unmatched are displayed ,if there is no data to be added on unmatched records null values are added and 9 unmatched records from left side table with null values when there is no data to be appended for tuples
  • 6(inner join matched records)+9(unmatched records from the left table)+3(unmatched records from the right table)=17 records (full outer join )

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