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What are different Types of Join?

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asked Mar 8, 2014 by smith Geek (15,340 points)

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Cross Join A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
Inner Join A join that displays only the rows that have a match in both joined tables is known as inner Join. This is the default type of join in the Query and View Designer.
Outer Join A join that includes rows even if they do not have related rows in the joined table is an Outer Join. You can create three different outer join to specify the unmatched rows to be included:
Left Outer Join: In Left Outer Join all rows in the first-named table i.e. "left" table, which appears leftmost in the JOIN clause are included. Unmatched rows in the right table do not appear.
Right Outer Join: In Right Outer Join all rows in the second-named table i.e. "right" table, which appears rightmost in the JOIN clause are included. Unmatched rows in the left table are not included.
Full Outer Join: In Full Outer Join all rows in all joined tables are included, whether they are matched or not.
Self Join This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company has a hierarchal reporting structure whereby one member of staff reports to another. Self Join can be Outer Join or Inner Join.
 
answered Mar 8, 2014 by kelly johnes Advisor (6,330 points)

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