Are you looking to join an industry as a DBMS developer? Have you prepared yourself to face DBMS interview questions? If not, then dig into some technical insights for DBMS. Database management has become popular more than ever. A set of logically arranged data for a specific purpose is commonly known as Database. A collection of programs, which can be used to create and maintain a database is known as Database Management System or DBMS. It is basically a systematic way of executing a command with data.
If one is through with the basics, half the battle is won. The more the knowledge on the subject, the easier will it be to crack the DBMS interview questions. There is a vast list of questionnaire available on Google to help you gain confidence before facing the interview panel.
CREATE table command- It defines each column of the table in a unique and distinct manner like name, data type, size, etc.
Syntax: CREATE TABLE [column name] ([column definitions]) [table parameters]
ALTER table command- ALTER is used to make changes and edit the existing table of database. Syntax: ALTER objecttype objectname parameters.
DROP table command – DROP is used for destroying a table and all the recorded data in it. It destroys an existing database. Syntax: DROP objecttype objectname parameters.
Join depicts the relationship between two or more tables. It combines row of different tables and enables you to select data with reference to data of some other table. There are several joins in database like CROSS JOINs, NATURAL JOINs, EQUI-JOIN, etc. Two most important joins are –
Nested loop- A nested loop is a loop within a loop. It is an inner loop within an outer body that allows fewer entries. Individual entries in nested loop is processed individually in the inner loop. Example-
.Select col.*, col2.* from coll, col2 where coll.coll=col2.col2;
The nested way works in following format-
For i in (select*from coll) loop
For j in (select*from col2 where col2 = i.coll) loop
Results are displayed
End of the loop;
End of the loop;
For nested loop, first outer (driving) table is identified. Then inner tavle is assigned to the outer table and every row in inner column is accessible from every row of outer table. Nested loop is executed from hash join, inner loop and then outer loop.
Hash join- it is divided into-
It is considered a better option as compared with nested loop when data volume is big. The full operation of hash join can be classified as-
Sort join operation-
Get first row R1 from input1 Get first row R2 from input2 Merge join operation- 'while' command is not used at loop's end. If R1 joins with R2 Next row is got R2 from the input2 Return (R1,R2) else if R1 ,style="". Next row is got from R1 from input1 else next row is got from R2 from input 2 end of the loop.
Atomicity: In database management, atomicity is a concept that assures the users of the incomplete transactions. It takes care of these transactions and the actions related to incomplete transactions are left undone in DBMS.
Aggregation: It aggregates the collected entities and their relationships. In this, information is gathered and expressed in summary form.
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