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Ans. Reliability and Continuity if some of the sites goes down.Easy Scaling up and Down as sites can be added or removed without impacting business continuity.
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Q32. When do we generally get this database error - integrity constraint violated - parent key not found ?
Ans. This error most likely will be thrown during an insert statement, while inserting a value within a foreign key column which doesnt exist within the Parent column. For example - Trying to add a dept number reference within a Employee Table when the Dept doesnt exist in the Dept Table.
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Ans. Stored procedures are a batch of SQL statements along with programming constructs ( if else, loops etc ) and stored as a single program that can be called by different clients and hence reused.
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Q36. There is a Table Student having Student Id, Name and Total Marks. Can you please write an SQL that will display the maximum marks obtained by a student ?
Q38. When do we generally get the database error - Unique Constraint Violated ?
Ans. This error can result either on an insert, update or delete when any change in data results in duplicate record or subset of it having unique constraint on record or its subset. For example - If we have a unique constraint on a combination of columns and then trying to insert duplicate column values.
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Ans. Audit Tables generally stores Raw information to be reviewed in case of problems or determining impact. If Database space is an issue , and the audit information is rarely retrieved, one design could be to use compressed file system.
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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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Ans. A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction but not yet committed.
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Ans. JDBC is a standard Java Api for Database communication whereas Hibernate is an ORM framework that uses JDBC to connect with Database.
Hibernate is another layer of object table mapping over JDBC that provide a database independent, object oriented and an efficient way of database communication.
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Which of the following is not true for Prepared Statements ?
Prepared Statements provides better performance
Prepared Statements prevent SQL Injection attacks
Prepared Statements provide ORM capabilities
Prepared Statement provides DB side caching
Q55. What are the benefits of using prepared statements ? Does that benefit extend only if similar prepared statements are used within a application or it extends even with multiple applications having similar prepared statement ?
Ans. Prepared Statements helps in reuse of database execution plan which can be cached at Database level and hence helps achieving faster execution and performance. As cached ps objects are creating at Database level and not application level, the use and benefit extends across multiple applications.
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Null value means that the value is yet to be assigned or need not be assigned whereas empty value means that the blank value has already been assigned once. Null is the default for the null able columns that hasn't be assigned any value.
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Ans. Application is unable to insert a record as it violates a unique constraint.
The exception states the constraint and Table can be located by the Entity mapping. So I will go to the DB and will first check to which all columns the unique constraint applies. And then I will go and check the code and logs to see how come the duplicate column values were attempted to be inserted when they were not supposed to be.
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Which of the following is not true for Prepared Statements ?
