sql joins explained - Wikitechy https://www.wikitechy.com/interview-questions/tag/sql-joins-explained/ Interview Questions Mon, 26 Sep 2022 09:35:23 +0000 en-US hourly 1 https://wordpress.org/?v=7.0 https://www.wikitechy.com/interview-questions/wp-content/uploads/2025/10/cropped-wikitechy-icon-32x32.png sql joins explained - Wikitechy https://www.wikitechy.com/interview-questions/tag/sql-joins-explained/ 32 32 What is a join in SQL ? What are the types of joins ? https://www.wikitechy.com/interview-questions/sql/what-is-a-join-in-sql-what-are-the-types-of-joins/ https://www.wikitechy.com/interview-questions/sql/what-is-a-join-in-sql-what-are-the-types-of-joins/#respond Mon, 26 Sep 2022 09:24:54 +0000 https://www.wikitechy.com/interview-questions/?p=4844
  • Data is stored in multiple tables that are related to each other in relational data bases like SQL Server, MySQL etc with a common key value.
  • When we need to get row by combining one or more tables based on common fields between them can be achieved using a SQL Join.
  • When we need to extract records from two or more tables into a new table, JOIN clause helps us to acheive this based on certain condition.
  • Based on logical relationship between tables join clause helps us to query and access data from multiple tables.
  • In other words, Join show how data from a row can be fetched from one table to another table.

    • Different types of Joins are:

    • Inner join/Simple Join
    • Left Outer join/Left Join
    • Right Outer Join/Right join
    • Full Outer join
    • Cross Join
    • Self Join

    Inner Join

    • In SQL if a defined condition is valid the inner join will select all the matching rows and columns from both tables.

    Syntax

    Select column_1, column_2 column_3 from table_1 innerjoin table_2 ON table_1.column = table_2.column;

    Left Join

    • In left join all records are retrived from left table(table1) and matched rows and column from right table(table2).
    • If there is no matching rows or columns, left join returns NULL.

    Syntax

    Select column_1, column_2, columns from Table_1 left join table_2 ON table_1.column_name = table_2.column name.

    Right Join or Right Outer Join

    • Records from the right table are retrived in RIGHT JOIN and the matched rows or columns from the left table(table1).
    • If there is no matching rows or columns it will return NULL.

    Syntax

    Select column_1, column_2, cloumn(s) FROM table_1 right join table_2 ON table_1.column_name= table2.column_name.

    Full Join or Full Outer Join

    • This join is a combination of both Left join and right join.
    • The joined tables returns all the records from both the tables.
    • If no matches are found in the table, this join will return a NULL Value.
    • It is also called as Full Outer Join.

    Syntax

    Select column_1, column_2, column(s) from table_1 Full join table_2 ON table_1.column_name = table_2.column_name;

    Cross Join

    • It is also known as Cartesian Join which returns cartesian product of two or more joined tables.
    • Cross join produces a table that merges each rows from the first table with each rows of second table.
    • No condition ir required for CROSS JOIN.

    Syntax

    Select * from table_1 cross join table_2;  
    Or,
    Select column1, column2, column3 from table_1, table_2;

    Self Join

    • Tables formed by joining itself is called Self Join.
    • It makes a temporary naming of atleast one table in SQL Statement.

    Syntax

    Select column1, column2, column(s) from table_1 Tbl1, table_2 Tbl2 where condition;

    ]]> https://www.wikitechy.com/interview-questions/sql/what-is-a-join-in-sql-what-are-the-types-of-joins/feed/ 0