ThoughtWorks Most Frequently Asked Latest SQL Server Interview Questions Answers
What is RDBMS?
RDBMS or Relational Data Base Management Systems are database management systems that maintain data in the form of tables. We can create relationships between the tables. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.
What are the properties of the Relational tables?
Relational tables have six properties:
Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.
What’s the difference between a primary key and a unique key?
The differences between primary key and a unique key are:
The primary key is a column whose values uniquely identify every row in a table. Primary key values can never be reused. They create a clustered index on the column and cannot be null.
A Unique key is a column whose values also uniquely identify every row in a table but they create a non-clustered index by default and it allows one NULL only.
When is UPDATE_STATISTICS command used?
As the name implies UPDATE_STATISTICS command updated the statistics used by the index to make the search easier.
What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
The differences between HAVING CLAUSE and WHERE CLAUSE are:
Both specify a search condition but Having clause is used only with the SELECT statement and typically used with GROUP BY clause.
If GROUP BY clause is not used then Having behaved like WHERE clause only.
Which TCP/IP port does SQL Server run on?
By default SQL Server runs on port 1433.
What is the difference between clustered and a non-clustered index?
A clustered index is an index that rearranges the table in the order of index itself. Its leaf nodes contain data pages. A table can have only one clustered index.
A non-clustered index is an index that does not re-arranges the table in the order of index itself. Its leaf nodes contain index rows instead of data pages. A table can have many non-clustered indexes.
List the different index configurations possible for a table?
A table can have one of the following index configurations:
No indexes
A clustered index
A clustered index and many non-clustered indexes
A non-clustered index
Many non-clustered indexes
What is the recovery model? List the types of recovery model available in SQL Server?
Recovery model basically tells SQL Server what data should be kept in the transaction log file and for how long. A database can have only one recovery model.
It also tells SQL server that which backup is possible in a particular recovery model selected. There are three types of recovery model:
Full
Simple
Bulk-Logged
Mirroring is a high availability solution. It is designed to maintain a hot standby server which is consistent with the primary server in terms of a transaction. Transaction Log records are sent directly from principal server to secondary server which keeps a secondary server up to date with the principal server.
What are the advantages of the Mirroring?
Advantages of Mirroring are:
It is more robust and efficient that Log shipping.
It has an automatic failover mechanism.
The secondary server is synced with the primary in near real time.
What is a Log Shipping?
Log shipping is nothing but the automation of backup and restores of a database from one server to another standalone standby server. This is one of the disaster recovery solutions. If one server fails for some reason we will have the same data available on the standby server.
What are the advantages of Log shipping?
Advantages of Log shipping:
Easy to set up.
Secondary database can be used as a read-only purpose.
Multiple secondary standby servers are possible
Low maintenance.
Can we take the full database backup in Log shipping?
Yes, we can take the full database backup. It won’t affect the log shipping.
What is an execution plan?
An execution plan is a graphical or textual way of showing how SQL server breaks down a query to get the required result. It helps a user to determine why queries are taking more time to execute and based on the investigation user can update their queries for the maximum result.
In Query Analyzer is an option called “Show Execution Plan” (located on the Query drop-down menu). If this option is turned on it will display a query execution plan in a separate window when a query is run again.
What is a performance monitor?
Windows performance monitor is a tool to capture metrics for the entire server. We can use this tool for capturing events of SQL server also.
Some useful counters are – Disks, Memory, Processors, Network etc.
What are 3 ways to get a count of the number of records in a table?
SELECT * FROM table_Name
SELECT COUNT(*) FROM table_Name
SELECT rows FROM indexes WHERE id = OBJECT_ID(tableName) AND indid< 2.
What is RDBMS?
RDBMS or Relational Data Base Management Systems are database management systems that maintain data in the form of tables. We can create relationships between the tables. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.
What are the properties of the Relational tables?
Relational tables have six properties:
Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.
What’s the difference between a primary key and a unique key?
The differences between primary key and a unique key are:
The primary key is a column whose values uniquely identify every row in a table. Primary key values can never be reused. They create a clustered index on the column and cannot be null.
A Unique key is a column whose values also uniquely identify every row in a table but they create a non-clustered index by default and it allows one NULL only.
When is UPDATE_STATISTICS command used?
As the name implies UPDATE_STATISTICS command updated the statistics used by the index to make the search easier.
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| ThoughtWorks Most Frequently Asked Latest SQL Server Interview Questions Answers |
What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
The differences between HAVING CLAUSE and WHERE CLAUSE are:
Both specify a search condition but Having clause is used only with the SELECT statement and typically used with GROUP BY clause.
If GROUP BY clause is not used then Having behaved like WHERE clause only.
Which TCP/IP port does SQL Server run on?
By default SQL Server runs on port 1433.
What is the difference between clustered and a non-clustered index?
A clustered index is an index that rearranges the table in the order of index itself. Its leaf nodes contain data pages. A table can have only one clustered index.
A non-clustered index is an index that does not re-arranges the table in the order of index itself. Its leaf nodes contain index rows instead of data pages. A table can have many non-clustered indexes.
List the different index configurations possible for a table?
A table can have one of the following index configurations:
No indexes
A clustered index
A clustered index and many non-clustered indexes
A non-clustered index
Many non-clustered indexes
What is the recovery model? List the types of recovery model available in SQL Server?
Recovery model basically tells SQL Server what data should be kept in the transaction log file and for how long. A database can have only one recovery model.
It also tells SQL server that which backup is possible in a particular recovery model selected. There are three types of recovery model:
Full
Simple
Bulk-Logged
What is Mirroring?
Mirroring is a high availability solution. It is designed to maintain a hot standby server which is consistent with the primary server in terms of a transaction. Transaction Log records are sent directly from principal server to secondary server which keeps a secondary server up to date with the principal server.
What are the advantages of the Mirroring?
Advantages of Mirroring are:
It is more robust and efficient that Log shipping.
It has an automatic failover mechanism.
The secondary server is synced with the primary in near real time.
What is a Log Shipping?
Log shipping is nothing but the automation of backup and restores of a database from one server to another standalone standby server. This is one of the disaster recovery solutions. If one server fails for some reason we will have the same data available on the standby server.
What are the advantages of Log shipping?
Advantages of Log shipping:
Easy to set up.
Secondary database can be used as a read-only purpose.
Multiple secondary standby servers are possible
Low maintenance.
Can we take the full database backup in Log shipping?
Yes, we can take the full database backup. It won’t affect the log shipping.
What is an execution plan?
An execution plan is a graphical or textual way of showing how SQL server breaks down a query to get the required result. It helps a user to determine why queries are taking more time to execute and based on the investigation user can update their queries for the maximum result.
In Query Analyzer is an option called “Show Execution Plan” (located on the Query drop-down menu). If this option is turned on it will display a query execution plan in a separate window when a query is run again.
What is a performance monitor?
Windows performance monitor is a tool to capture metrics for the entire server. We can use this tool for capturing events of SQL server also.
Some useful counters are – Disks, Memory, Processors, Network etc.
What are 3 ways to get a count of the number of records in a table?
SELECT * FROM table_Name
SELECT COUNT(*) FROM table_Name
SELECT rows FROM indexes WHERE id = OBJECT_ID(tableName) AND indid< 2.
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