DBMS Interview Questions and Answers
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Related differences
Ques 21. What is “CROSS JOIN”? or What is Cartesian product?
“CROSS JOIN” or “CARTESIAN PRODUCT” combines all rows from both tables. Number of rows will be product of the number of rows in each table. In real life scenario I can not imagine where we will want to use a Cartesian product. But there are scenarios where we would like permutation and combination probably Cartesian would be the easiest way to achieve it.
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Ques 22. How to select the first record in a given set of rows?
Select top 1 * from wb.wbEmployees;
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Ques 23. What is the default “-SORT ” order for a SQL?
ASCENDING
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Ques 24. What is a self-join?
If we want to join two instances of the same table we can use self-join.
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Ques 25. What’s the difference between DELETE and TRUNCATE?
Following are difference between them:
- DELETE TABLE syntax logs the deletes thus making the delete operations low. TRUNCATE table does not log any information but it logs information about deallocation of data page of the table. So TRUNCATE table is faster as compared to delete table.
- DELETE table can have criteria while TRUNCATE can not.
- TRUNCATE table can not have triggers.
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