What is a join? Explain different types of joins?
Answers were Sorted based on User's Feedback
Answer / nareshkumar
A join is a condition that links the data in seperate but
related tables. The tables usually have a parent-child
relationship. If a query does not contain a join, the
database returns a result set that contains all possible
combinations of the rows in the query tables.
Types of joins:
1) Equi-Joins
Link tables based on the equality between the values in the
column of one table and the values in the column of another.
2) Theta Joins
Link tables based on a relationship other than equality
between two columns.
3) Outer Joins (Left Outer, Right Outer, Full Outer)
Link two tables, one of which has rows that do not match
those in the common column of the other table.
4) Shortcut Joins
Join providing an alternative path between two tables,
bypassing intermediate tables, leading to the same result,
regardless of direction. Optimizes query time by cutting
long join paths as short as possible.
5) Self restricting joins
Single table join used to set a restriction on the table.
Is This Answer Correct ? | 24 Yes | 4 No |
Answer / subhash
Join is used to link to tables depending upon the data
requested by the user, Usually we have Inner Join, Outer
Join, Left Join, Right Join, Full Outer join.
Is This Answer Correct ? | 14 Yes | 5 No |
Answer / vams_gk
join is very imp concept in BO
relation between two tables is called joins.
we have 4 types of join relations 1:m,m:1,m:m,1:1
types of joins in BO
1)equi join
2)theta join
3)outer join(left/right)
4)isolated join
5)short cut join
Is This Answer Correct ? | 11 Yes | 2 No |
Answer / venkatesh
Hi everybody,
whatever NareshKumar explained about the joins is right
except the Shortcut join.
4) Shortcut Joins
Join providing an alternative path between two tables,
bypassing intermediate tables, "leading to the same result,
regardless of direction". Optimizes query time by cutting
long join paths as short as possible.
In the above defination (which is mentioned in the inverted
commas)the result wont be same. It is different.
Example:
There is 4 tables
A,B,C,D
The join in between these 4 tables are like this.
A--B--C--D
Here if I drag A and D tables then I will get 6 rows for
example.
Now Make a shortcut join between A and D
Now if I drag A and D tables then I will get more than 6
rows.Why because
In first join the data is filtering from A to D like below
First A to B then B to C after that C to D.
But in Shortcut there is direct join A to D.Here the data
is not filtering.
Thanks,
Venky
Is This Answer Correct ? | 5 Yes | 3 No |
Answer / srinu
Combining a data from multiple tables is called join.
There r 5 types of joins r there.
1)Simple join 2)Equi join 3)Outer join 4)Theta join
5)Short cut join
Is This Answer Correct ? | 4 Yes | 11 No |
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