Inner Join

January 27, 2023

About Inner Join in DBMS

In this article, we will learn about the inner join in DBMS.
Inner Join between two tables helps to retrieve data that will be common to both the tables and thus also referred to as equi
join or simple join.

 

Inner join in DBMS

Inner Join in SQL

 

  • Joins enable data merging from multiple tables
  • Inner join is also called an equi join or simple join.
Inner Join in DBMS
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Functional Dependencies

Joins in DBMS

Relational Algebra

Deadlock in DBMS

Definition of Inner Join

  • Based on the equality condition data is retrieved from multiple tables
  • We must have a common column in both tables with the same data type.

Syntax

select col1,col2 
from
table1,tabel2
where table1.comcolname=table2.comcolname;

Inner join Example

Consider two tables :

emp table
EMPNO ENAME JOB MGR HIREDATE 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-FEBc-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

InnerJoin SQL query

select ename,sal,dept.deptno,dname,dname,loc 
from emp,dept 
where emp.deptno=dept.deptno;
O/P
ROWNUM ENAME SAL DEPTNO DNAME DNAME LOC
1 KING 5000 10 ACCOUNTING ACCOUNTING NEW YORK
2 BLAKE 2850 30 SALES SALES CHICAGO
3 CLARK 2450 10 ACCOUNTING ACCOUNTING NEW YORK
4 JONES 2975 20 RESEARCH RESEARCH DALLAS
5 SCOTT 3000 20 RESEARCH RESEARCH DALLAS
6 FORD 3000 20 RESEARCH RESEARCH DALLAS
7 SMITH 800 20 RESEARCH RESEARCH DALLAS
8 ALLEN 1600 30 SALES SALES CHICAGO
9 WARD 1250 30 SALES SALES CHICAGO
10 MARTIN 1250 30 SALES SALES CHICAGO
11 TURNER 1500 30 SALES SALES CHICAGO
12 ADAMS 1100 20 RESEARCH RESEARCH DALLAS
13 JAMES 950 30 SALES SALES CHICAGO
14 MILLER 1300 10 ACCOUNTING ACCOUNTING NEW YORK
For each and every row in emp table, there is a match with any of the deptno in dept table hence the 14 rows are displayed

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