INTERVIEW QUESTIONS ORACLE SQL PLUS DETAILS

Question: What is a join ? Explain the different types of joins ?

Answer: Join is a query which retrieves related columns or rows from multiple tables.Self Join - Joining the table with itself.Equi Join - Joining two tables by equating two common columns.Non-Equi Join - Joining two tables by equating two common columns.Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table.

Join is a query which retrieves related columns or rows from multiple tables.Self Join - Joining the table with itself.Equi Join - Joining two tables by equating two common columns.Non-Equi Join - Joining two tables by equating two common columns.Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table. Source: CoolInterview.com

JOIN: Return rows when there is at least one match in both tables
LEFT JOIN: Return all rows from the left table, even if there are no matches in the right table
RIGHT JOIN: Return all rows from the right table, even if there are no matches in the left table
FULL JOIN: Return rows when there is a match in one of the tables
Source: CoolInterview.com

Joining multiple tables(Equi join).
Joining a table to itself(self join).
JOIN CAN BE DONE by USING and ON CLAUSE.equi join is a inner join and a join where + operator is used to return unmatched row known as outer join. 'Not exists' is also used to performed join. Source: CoolInterview.com

inner join retrieves all matched records from tables

take two tables
(t1 -left table and t2 -right table)
left join retrieves all matched records from tables(t1 union(t1 intersect t2) Source: CoolInterview.com

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