1) What are advantages and Disadvantages of Indexes?
2) What will be output of below Query for the following tables?
Table: A Table: B
SELECT * FROM A INNER JOIN B ON A.id=B.ID
Answer : Output of above query will be shown in below screenshot.
3) What are the Magic Tables?
Magic Tables are those tables which are shown as Inserted and Deleted Tables in Trigger.
l If you insert data in table to implement Trigger , That Inserted Tables will be as Inserted Magic Tables.
l If you delete data from table to implement Trigger , That Deleted Tables will be as Deleted Magic Tables.
Create Trigger T1
Select * from INSERTED
In above query INSERTED table will be Magic Table Just like DELETED Tables.
4) What is the ACID Properties?
Answer: ACID stands for Atomicity Consistency Isolation Durability
Atomicity: All transactions should be complete or none (Rolled back)
Ex : If we are running two query . one is correct and other is wrong , then both will be rolled back.
If both query are correct , both will succeeded
Consistency : Data should be in consistent state
Ex : If we are updating data by using one query suddenly there is a system failure (right before the insertion into sales or in the middle).
In this situation system will rollback the updates Otherwise, you can’t trace out the stock information.
Isolation: Transaction are independent
Ex : If we begin one transaction to update data in single statement and Other query also executed after in other window then it will not return data .
One transaction can’t access the result of other transaction until the transaction is completed.
Durability: Committed data is never lost
Once the transaction is successfully completed, then the changes it has made to the database will be permanent.
Even if there is a system failure, or any abnormal changes also, this SQL acid property will safeguard the committed data.
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