SQL Joins - The Coding Shala

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SQL Joins

The SQL Join Clause is used to combine records from two or more tables based on some common columns.
SQL Joins - The Coding Shala

Example

Table 1.  'emp' table - 

 emp_id     emp_name     city     dept_no     salary  
 1          Akshay        Pune      101       50000  
 3          Nikhil        Pune      101       51000  
 5          Mohit         Delhi     103       40000  
 6          Shubham       Surat     105       42000  
 7          Akash         Mumbai    106       45000

Table 2. 'dept' table - 

dept_no     dept_name      total_emp  
 101          Product Dev       50  
 102          Consulting       100  
 103          Product Consult   20  
 104          Marketing        150  
 105          Sales            250

The following SQL query will select the records where dept_no is same on both the tables - 

SQL >> select emp.emp_id, emp.emp_name, emp.salary, emp.dept_no, dept.dept_name  
        from emp, dept  
        where emp.dept_no = dept.dept_no;  
 Output >>   
 emp_id     emp_name     salary     dept_no     dept_name  
 1          Akshay         50000     101      Product Dev  
 3          Nikhil         51000     101      Product Dev  
 5          Mohit          40000     103      Product Consult  
 6          Shubham       42000      105      Sales

Types of SQL JOINs 

Following are the different types of Joins in SQL - 
  • INNER JOIN - Return records that have matching values in both the tables.
  • LEFT (OUTER) JOIN - Return all the rows from the left table, even if there are no matches in the right table.
  • RIGHT (OUTER) JOIN - Return all the rows from the right table, even if there are no matches in the left table.
  • FULL (OUTER) JOIN - Return all the rows when there is a match either on the left or right table.
  • SELF JOIN - is used to join a table to itself.
  • CARTESIAN JOIN - Return the cartesian product of the sets of rows from the joined tables.



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