Persistent Systems Most Frequently Asked Latest SQL Server Interview Questions Answers
What are Constraints or Define Constraints ?
Generally we use Data Types to limit the kind of Data in a Column. For example, if we declare any column with data type INT then ONLY Integer data can be inserted into the column. Constraint will help us to limit the Values we are passing into a column or a table. In simple Constraints are nothing but Rules or Conditions applied on columns or tables to restrict the data.
Different types of Constraints ?
There are THREE Types of Constraints.
Domain
Entity
Referential
Domain has the following constraints types –
Not Null
Check
Entity has the following constraint types –
Primary Key
Unique Key
Referential has the following constraint types –
Foreign Key
Types of Indices in SQL ?
There are TWO types of Indices in SQL server.
Clustered
Non Clustered
How many Clustered and Non Clustered Indexes can be defined for a table ?
Clustered – 1
Non Clustered – 999
What is Transaction in SQL Server ?
Transaction groups a set of T-Sql Statements into a single execution unit. Each transaction begins with a specific task and ends when all the tasks in the group successfully complete. If any of the tasks fails, the transaction fails. Therefore, atransaction has only two results: success or failure. Incomplete steps result in the failure of the transaction.by programmers to group together read and write operations. In Simple Either FULL or NULL i.e either all the statements executes successfully or all the execution will be rolled back.
Types of Transactions ?
There are TWO forms of Transactions.
Implicit – Specifies any Single Insert,Update or Delete statement as Transaction Unit. No need to specify Explicitly.
Explicit – A group of T-Sql statements with the beginning and ending marked with Begin Transaction,Commit and RollBack. PFB an Example for Explicit transactions.
BEGIN TRANSACTION
Update Employee Set Emp_ID = 54321 where Emp_ID = 12345
If(@@Error <>0)
ROLLBACK
Update LEave_Details Set Emp_ID = 54321 where Emp_ID = 12345
If(@@Error <>0)
ROLLBACK
COMMIT
In the above example we are trying to update an EMPLOYEE ID from 12345 to 54321 in both the master table “Employee” and Transaction table “Leave_Details”. In this case either BOTH the tables will be updated with new EMPID or NONE.
What is the Max size and Max number of columns for a row in a table ?
Size – 8060 Bytes
Columns – 1024
What is Normalization and Explain different normal forms.
Database normalization is a process of data design and organization which applies to data structures based on rules that help building relational databases.
1. Organizing data to minimize redundancy.
2. Isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.
1NF: Eliminate Repeating Groups
Each set of related attributes should be in separate table, and give each table a primary key. Each field contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
1. Table must be in 1NF.
2. All fields are dependent on the whole of the primary key, or a relation is in 2NF if it is in 1NF and every non-key attribute is fully dependent on each candidate key of the relation. If an attribute depends on only part of a multi‐valued key, remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
1. The table must be in 2NF.
2. Transitive dependencies must be eliminated. All attributes must rely only on the primary key. If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary key.
BCNF: Boyce‐Codd Normal Form
for every one of its non-trivial functional dependencies X → Y, X is a superkey—that is, X is either a candidate key or a superset thereof. If there are non‐trivial dependencies between candidate key attributes, separate them out into distinct tables.
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not directly related.
For example, if you can have two phone numbers values and two email address values, then you should not have them in the same table.
5NF: Isolate Semantically Related Multiple Relationships
A 4NF table is said to be in the 5NF if and only if every join dependency in it is implied by the candidate keys. There may be practical constrains on information that justify separating logically related many‐to‐many relationships.
What is Temporary table ?
A temporary table is a database object that is temporarily stored and managed by the database system. There are two types of Temp tables.
Local
Global
What are the differences between Local Temp table and Global Temp table ?
Before going to the differences, let’s see the similarities.
Both are stored in tempdb database.
Both will be cleared once the connection,which is used to create the table, is closed.
Both are meant to store data temporarily.
PFB the differences between these two.
Local temp table is prefixed with # where as Global temp table with ##.
Local temp table is valid for the current connection i.e the connection where it is created where as Global temp table is valid for all the connection.
Local temp table cannot be shared between multiple users where as Global temp table can be shared.
What are the differences between WHERE and HAVING clauses in SQl Server ?
PFB the major differences between WHERE and HAVING Clauses ..
1.Where Clause can be used other than Select statement also where as Having is used only with the SELECT statement.
2.Where applies to each and single row and Having applies to summarized rows (summarized with GROUP BY).
3.In Where clause the data that fetched from memory according to condition and In having the completed data firstly fetched and then separated according to condition.
4.Where is used before GROUP BY clause and HAVING clause is used to impose condition on GROUP Function and is used after GROUP BY clause in the query.
Explain Physical Data Model or PDM ?
Physical data model represents how the model will be built in the database. A physical database model shows all table structures, including column name, column data type, column constraints, primary key, foreign key, and relationships between tables. Features of a physical data model include:
Specification all tables and columns.
Foreign keys are used to identify relationships between tables.
Specying Data types.
EG –
Explain Logical Data Model ?
A logical data model describes the data in as much detail as possible, without regard to how they will be physical implemented in the database. Features of a logical data model include:
Includes all entities and relationships among them.
All attributes for each entity are specified.
The primary key for each entity is specified.
Foreign keys (keys identifying the relationship between different entities) are specified.
Normalization occurs at this level.
Explain Conceptual Data Model ?
A conceptual data model identifies the highest-level relationships between the different entities. Features of conceptual data model include:
Includes the important entities and the relationships among them.
No attribute is specified.
No primary key is specified.
What is Log Shipping ?
Log Shipping is a basic level SQL Server high-availability technology that is part of SQL Server. It is an automated backup/restore process that allows you to create another copy of your database for failover.
Log shipping involves copying a database backup and subsequent transaction log backups from the primary (source) server and restoring the database and transaction log backups on one or more secondary (Stand By / Destination) servers. The Target Database is in a standby or no-recovery mode on the secondary server(s) which allows subsequent transaction logs to be backed up on the primary and shipped (or copied) to the secondary servers and then applied (restored) there.
What are Constraints or Define Constraints ?
Generally we use Data Types to limit the kind of Data in a Column. For example, if we declare any column with data type INT then ONLY Integer data can be inserted into the column. Constraint will help us to limit the Values we are passing into a column or a table. In simple Constraints are nothing but Rules or Conditions applied on columns or tables to restrict the data.
Different types of Constraints ?
There are THREE Types of Constraints.
Domain
Entity
Referential
Domain has the following constraints types –
Not Null
Check
Entity has the following constraint types –
Primary Key
Unique Key
Referential has the following constraint types –
Foreign Key
Types of Indices in SQL ?
There are TWO types of Indices in SQL server.
Clustered
Non Clustered
How many Clustered and Non Clustered Indexes can be defined for a table ?
Clustered – 1
Non Clustered – 999
What is Transaction in SQL Server ?
Transaction groups a set of T-Sql Statements into a single execution unit. Each transaction begins with a specific task and ends when all the tasks in the group successfully complete. If any of the tasks fails, the transaction fails. Therefore, atransaction has only two results: success or failure. Incomplete steps result in the failure of the transaction.by programmers to group together read and write operations. In Simple Either FULL or NULL i.e either all the statements executes successfully or all the execution will be rolled back.
Types of Transactions ?
There are TWO forms of Transactions.
Implicit – Specifies any Single Insert,Update or Delete statement as Transaction Unit. No need to specify Explicitly.
Explicit – A group of T-Sql statements with the beginning and ending marked with Begin Transaction,Commit and RollBack. PFB an Example for Explicit transactions.
BEGIN TRANSACTION
Update Employee Set Emp_ID = 54321 where Emp_ID = 12345
If(@@Error <>0)
ROLLBACK
Update LEave_Details Set Emp_ID = 54321 where Emp_ID = 12345
If(@@Error <>0)
ROLLBACK
COMMIT
In the above example we are trying to update an EMPLOYEE ID from 12345 to 54321 in both the master table “Employee” and Transaction table “Leave_Details”. In this case either BOTH the tables will be updated with new EMPID or NONE.
What is the Max size and Max number of columns for a row in a table ?
Size – 8060 Bytes
Columns – 1024
What is Normalization and Explain different normal forms.
Database normalization is a process of data design and organization which applies to data structures based on rules that help building relational databases.
1. Organizing data to minimize redundancy.
2. Isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.
1NF: Eliminate Repeating Groups
Each set of related attributes should be in separate table, and give each table a primary key. Each field contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
1. Table must be in 1NF.
2. All fields are dependent on the whole of the primary key, or a relation is in 2NF if it is in 1NF and every non-key attribute is fully dependent on each candidate key of the relation. If an attribute depends on only part of a multi‐valued key, remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
1. The table must be in 2NF.
2. Transitive dependencies must be eliminated. All attributes must rely only on the primary key. If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary key.
BCNF: Boyce‐Codd Normal Form
for every one of its non-trivial functional dependencies X → Y, X is a superkey—that is, X is either a candidate key or a superset thereof. If there are non‐trivial dependencies between candidate key attributes, separate them out into distinct tables.
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not directly related.
For example, if you can have two phone numbers values and two email address values, then you should not have them in the same table.
5NF: Isolate Semantically Related Multiple Relationships
A 4NF table is said to be in the 5NF if and only if every join dependency in it is implied by the candidate keys. There may be practical constrains on information that justify separating logically related many‐to‐many relationships.
What is Temporary table ?
A temporary table is a database object that is temporarily stored and managed by the database system. There are two types of Temp tables.
Local
Global
 |
| Persistent Systems Most Frequently Asked Latest SQL Server Interview Questions Answers |
What are the differences between Local Temp table and Global Temp table ?
Before going to the differences, let’s see the similarities.
Both are stored in tempdb database.
Both will be cleared once the connection,which is used to create the table, is closed.
Both are meant to store data temporarily.
PFB the differences between these two.
Local temp table is prefixed with # where as Global temp table with ##.
Local temp table is valid for the current connection i.e the connection where it is created where as Global temp table is valid for all the connection.
Local temp table cannot be shared between multiple users where as Global temp table can be shared.
What are the differences between WHERE and HAVING clauses in SQl Server ?
PFB the major differences between WHERE and HAVING Clauses ..
1.Where Clause can be used other than Select statement also where as Having is used only with the SELECT statement.
2.Where applies to each and single row and Having applies to summarized rows (summarized with GROUP BY).
3.In Where clause the data that fetched from memory according to condition and In having the completed data firstly fetched and then separated according to condition.
4.Where is used before GROUP BY clause and HAVING clause is used to impose condition on GROUP Function and is used after GROUP BY clause in the query.
Explain Physical Data Model or PDM ?
Physical data model represents how the model will be built in the database. A physical database model shows all table structures, including column name, column data type, column constraints, primary key, foreign key, and relationships between tables. Features of a physical data model include:
Specification all tables and columns.
Foreign keys are used to identify relationships between tables.
Specying Data types.
EG –
Explain Logical Data Model ?
A logical data model describes the data in as much detail as possible, without regard to how they will be physical implemented in the database. Features of a logical data model include:
Includes all entities and relationships among them.
All attributes for each entity are specified.
The primary key for each entity is specified.
Foreign keys (keys identifying the relationship between different entities) are specified.
Normalization occurs at this level.
Explain Conceptual Data Model ?
A conceptual data model identifies the highest-level relationships between the different entities. Features of conceptual data model include:
Includes the important entities and the relationships among them.
No attribute is specified.
No primary key is specified.
What is Log Shipping ?
Log Shipping is a basic level SQL Server high-availability technology that is part of SQL Server. It is an automated backup/restore process that allows you to create another copy of your database for failover.
Log shipping involves copying a database backup and subsequent transaction log backups from the primary (source) server and restoring the database and transaction log backups on one or more secondary (Stand By / Destination) servers. The Target Database is in a standby or no-recovery mode on the secondary server(s) which allows subsequent transaction logs to be backed up on the primary and shipped (or copied) to the secondary servers and then applied (restored) there.
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