Database - Interview Questions and Answers for 'Amd' | Search Interview Question

Database - Interview Questions and Answers for 'Amd' - 3 question(s) found - Order By Newest

Q1. What is the purpose of Commit and Rollback in Databases ?

Ans. When a DML is executed, the changes only stays in session and still not pushed to DB Tables, Commit is used to push those changes to the Tables.

In case we realize that we don't want to commit those changes and would like to ignore them, we can use rollback.

For example - You may like that for a banking transaction you would like to update the account balance only if the debit or credit record was correctly inserted, so you may like to encapsulate both DML's - insert for transaction and update for balance in a single transaction and would only commit if both succeeds else rollback.

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Q2. What are the methods to connect to database in Java ?

Database

Ans. JDBC ( Java Database Connectivity ),ODBC (Open Database Connectivity), Hibernate, JPA ( Java Persistence API ), JOOQ,MyBatis

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Related Questions

What is database deadlock ? How can we avoid them?

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What things you would care about to improve the performance of Application if its identified that its DB communication that needs to be improved ?

If you are given a choice to implement the code to either Insert a Record or Update if already exist, Which approach will you follow ?

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What is a Database Trigger ?

What happens to backups if we delete the RDS instance ?

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Q3. Write a SQL to delete duplicate records in a table

Database

Ans. DELETE FROM TABLE WHERE ROW_NUM NOT IN ( SELECT MAX(ROW_ID) FROM TABLE GROUP BY DUPLICATE_FIELD )

or

DELETE FROM TABLE a WHERE ROW_ID >(SELECT MIN(ROW_ID FROM TABLE b WHERE a.DUPLICATE_FIELD=b.DUPLICATE_FIELD);

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