types of SQL Joins
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The document explains various types of SQL joins used to retrieve data from multiple tables based on column relationships. It covers inner joins, left joins, right joins, full joins, and self joins, including their syntax and example queries. Each join type is presented with scenarios showing how they operate regarding matched and unmatched rows.
types of SQL Joins
- 2. Prepared by; name en.number • Vikram rajpurohit 140500116033 • Taxak mistery 140500116016 • Paras patel 140500116024
- 3. SQL Joins SQL joins are used to get data from two or more tables bases on relationship between some of the columns in tables. In most of the cases we will use primary key of first table and foreign key of secondary table to get data from tables
- 5. Tables for examples EMPNO ENAME JOB MGR DEPTNO 111 Ramesh Analyst 444 10 222 Khilan Clerk 333 20 333 Kaushik Manager 111 10 444 Chaitali engineer 222 40 DEPTNO DNAME LOC 10 INVENTORY HYDERABAD 20 FINANCE BANGALORE 30 HR MUMBAI
- 6. INNER JOIN OR EQUIJOIN clause is used to combine rows from two or more tables, based on a common field between them. INNER JOIN creates a new result table by combining column values of two tables (table1 and table2) based upon the join-condition. Keyword used is INNER JOIN or simply JOIN.
- 7. INNER JOIN OR EQUIJOIN Syntax SELECT table1.column1, table2.column2... FROM table1 INNER JOIN table2 ON table1.common_field = table2.common_field; SELECT emp.ename,emp.job,dept.dname,dept.loc from EMPLOYYE emp INNER JOIN DEPARTMENT dept ON emp.deptno = dept.deptno;
- 8. Result…… ENAME JOB DNAME LOC Ramesh Analyst INVENTORY HYDERABAD Khilan Clerk FINANCE BANGALORE Kaushik Manager INVENTORY HYDERABAD
- 9. Left Join/Left Outer Join LEFT JOIN returns all rows from the left table (table1), even if there are no matches in the right table(table2). If there are no matches found in right table the result is null in the right table. Keyword used is LEFT JOIN.
- 10. Left Join Continuation… Syntax SELECT table1.column1, table2.column2... FROM table1 LEFT JOIN table2 ON table1.common_field = table2.common_field; SELECT emp.ename,emp.job,dept.dname,dept.loc from EMPLOYYE emp LEFT JOIN DEPARTMENT dept ON emp.deptno = dept.deptno; OR SELECT emp.ename,emp.job,dept.dname,dept.loc from EMPLOYYE emp , DEPARTMENT dept WHERE emp.deptno(+) = dept.deptno; ENAME JOB DNAME LOC Ramesh Analyst INVENTORY HYDERABAD Khilan Clerk FINANCE BANGALORE Kaushik Manager INVENTORY HYDERABAD Chaitali engineer NULL NULL
- 11. Right Join/Right Outer Join RIGHT JOIN returns all rows from the right table (table2), even if there are no matches in the left table(table1). If there are no matched found in let table the result is null in the left table. Keyword used is RIGHT JOIN.
- 12. Right Join Continuation… Syntax SELECT table1.column1, table2.column2... FROM table1 RIGHT JOIN table2 ON table1.common_field = table2.common_field; SELECT emp.ename,emp.job,dept.dname,dept.loc from EMPLOYYE emp RIGHT JOIN DEPARTMENT dept ON emp.deptno = dept.deptno; OR SELECT emp.ename,emp.job,dept.dname,dept.loc from EMPLOYYE emp, DEPARTMENT dept WHERE emp.deptno = dept.deptno(+); ENAME JOB DNAME LOC Ramesh Analyst INVENTORY HYDERABAD Khilan Clerk FINANCE BANGALORE Kaushik Manager INVENTORY HYDERABAD NULL NULL HR MUMBAI
- 13. Full Join The SQL FULL JOIN combines the results of both left and right outer joins. The joined table will contain all records from both tables, and fill in NULLs for missing matches on either side. Keyword used is FULL JOIN. In some data bases it is also known as FULL OUTER JOIN.
- 14. Full Join Continuation… Syntax SELECT table1.column1, table2.column2... FROM table1 FULL JOIN table2 ON table1.common_field = table2.common_field; SELECT emp.ename,emp.job,dept.dname,dept.loc from EMPLOYYE emp FULL JOIN DEPARTMENT dept ON emp.deptno = dept.deptno; ENAME JOB DNAME LOC Ramesh Analyst INVENTORY HYDERABAD Khilan Clerk FINANCE BANGALORE Kaushik Manager INVENTORY HYDERABAD NULL NULL HR MUMBAI Chaitali engineer NULL NULL
- 15. Self Join SELF JOIN is used to join a table to itself as if the table were two tables Syntax SELECT a.column_name, b.column_name... FROM table1 a, table1 b WHERE a.common_field = b.common_field;
- 16. Self Join Continuation…. SELECT emp1.ename, emp1.job, emp2.ename as manager FROM EMPLOYEE emp1, EMPLOYEE emp2 where emp1.mgr = emp2.empno; ENAME JOB MANAGER Ramesh Analyst Chaitali Khilan Clerk Kaushik Kaushik Manager Ramesh Chaitali engineer Khilan