There are basically two types of indexes:- Clustered Indexes. Non-Clustered Indexes. In clustered index the non-leaf level actually points to the actual data.In Non-Clustered index the leaf nodes point to pointers (they are rowid’s) which then point to actual data. The correct answer to your question would be the difference between clustered and non-clustered indexes. Clustered Index: A clustered index determines the physical order of data rows in a table based on the indexed column(s). Each table can have only…

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Data Warehousing” is technical process where we are making our data centralized while “Data mining” is more of business activity which will analyze how good your business is doing or predict how it will do in the future coming times using the current data. As said before “Data Warehousing” is not a need for “Data mining”. It’s good if you are doing “Data mining” on a “Data Warehouse” rather than on an actual production database. “Data Warehousing” is essential when…

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“HAVING” clause is used to specify filtering criteria for “GROUP BY”, while “WHERE” clause applies on normal SQL. The “WHERE” and “HAVING” clauses in a database management system (DBMS) both filter data, but they operate at different stages of the query process and are used for different purposes. WHERE Clause: The “WHERE” clause is used to filter rows before any groupings are made. It is used with the “SELECT”, “UPDATE”, and “DELETE” statements to specify the conditions that must be…

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ASCENDING In SQL, there’s no default “-SORT” order. Sorting in SQL is explicitly specified using the ORDER BY clause. If you don’t specify an ORDER BY clause, the result set’s order is not guaranteed. However, some database management systems might return results in the order they were inserted or some other internal ordering, but this behavior is not consistent across different systems and should not be relied upon. So, in short, there’s no default “-SORT” order in SQL.

INNER JOIN Inner join shows matches only when they exist in both tables. Example in the below SQL there are two tables Customers and Orders and the inner join in made on Customers.Customerid and Orders.Customerid. So this SQL will only give you result with customers who have orders. If the customer does not have order it will not display that record. SELECT Customers.*, Orders.* FROM Customers INNER JOIN Orders ON Customers.CustomerID =Orders.CustomerID LEFT OUTER JOIN Left join will display all…

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ORDER BY clause helps to sort the data in either ascending order to descending order. Ascending order sort query: SELECT name,age FROM pcdsEmployee ORDER BY age ASC Descending order sort query SELECT name FROM pcdsEmployee ORDER BY age DESC The correct answer for “What is the ORDER BY clause in a database management system (DBMS)?” would be: “The ORDER BY clause is used in SQL (Structured Query Language) to sort the result set of a query in ascending or descending…

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In 1969 Dr. E. F. Codd laid down some 12 rules which a DBMS should adhere in order to get the logo of a true RDBMS. Rule 1: Information Rule. “All information in a relational data base is represented explicitly at the logical level and in exactly one way – by values in tables.” Rule 2: Guaranteed access Rule. “Each and every datum (atomic value) in a relational data base is guaranteed to be logically accessible by resorting to a…

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Database provides a systematic and organized way of storing, managing and retrieving from collection of logically related information. Secondly the information has to be persistent, that means even after the application is closed the information should be persisted. Finally it should provide an independent way of accessing data and should not be dependent on the application to access the information. Main difference between a simple file and database that database has independent way (SQL) of accessing information while simple files…

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What is System R? How many of its two major subsystems? System R was designed and developed from 1974 to 1979 at IBM San Jose Research Centre. System R is the first implementation of SQL, which is the standard relational data query language, and it was also the first to demonstrate that RDBMS could provide better transaction processing performance. It is a prototype which is formed to show that it is possible to build a Relational System that can be…

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What do you mean by extension and intension? Extension: The Extension is the number of tuples present in a table at any instance. It changes as the tuples are created, updated and destroyed. The actual data in the database change quite frequently. So, the data in the database at a particular moment in time is known as extension or database state or snapshot. It is time dependent. Intension: Intension is also known as Data Schema and defined as the description of the…

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