Database Joins Tutorial Pdf
It is used for combining column from two or more tables by using values common to both tables. All the tuples from both participating relations are included in the resulting relation. We can perform a Natural Join only if there is at least one common attribute that exists between two relations. In addition, the attributes must have the same name and domain. Theta join combines tuples from different relations provided they satisfy the theta condition.
Natural Join is a type of Inner join which is based on column having same name and same datatype present in both the tables to be joined. As you can see, this join returns the cross product of all the records present in both the tables. But it might not be feasible for us in certain cases to take a Cartesian product where we encounter huge relations with thousands of tuples having a considerable large number of attributes. All the tuples from the Left relation, R, are included in the resulting relation. We understand the benefits of taking a Cartesian product of two relations, which gives us all the possible tuples that are paired together.
The right outer join returns a resultset table with the matched data from the two tables being joined, then the remaining rows of the right table and null for the remaining left table's columns.
SQL JOIN - Inner Outer Left and Right Join
The left outer join returns a resultset table with the matched data from the two tables and then the remaining rows of the left table and null from the right table's columns. Join is a combination of a Cartesian product followed by a selection process. Natural join acts on those matching attributes where the values of attributes in both the relations are same. An inner join includes only those tuples with matching attributes and the rest are discarded in the resulting relation. Natural join does not use any comparison operator.
The above example corresponds to equijoin. It will return a table which consists of records which combines each row from the first table with each row of the second table.
Theta Join, Equijoin, and Natural Join are called inner joins. Therefore, we need to use outer joins to include all the tuples from the participating relations in the resulting relation. The full outer join returns a resultset table with the matched data of two table then remaining rows of both left table and then the right table. It does not concatenate the way a Cartesian product does. All the tuples from the Right relation, S, boy scout eagle project pdf are included in the resulting relation.
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