SQL Server Interview Question Part 2

Q1. Which TCP/IP port does SQL Server run on? How can it be changed?

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties.

Q2. How is ACID property related to Database?

ACID (an acronym for Atomicity Consistency Isolation Durability) is a concept that Database Professionals generally look for while evaluating databases and application architectures. For a reliable database, all this four attributes should be achieved.

1. Atomicity is an all-or-none proposition.
2. Consistency guarantees that a transaction never leaves your database in a half-finished state.
3. Isolation keeps transactions separated from each other until they are finished.
4. Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination

Q3. What's the difference between a primary key and a unique key?

Both primary key and unique key enforces uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

Q4. What are Primary Keys and Foreign Keys?

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental aspect of all keys and constraints. A table can have only one primary key.

Foreign keys are a method of ensuring data integrity and manifestation of the relationship between tables.

Q5. What are the difference between clustered and a non-clustered index?

1. A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
2. A non-clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.     

Q6. What are the different index configurations a table can have?

A table can have one of the following index configurations:

1. No indexes
2. A clustered index
3. A clustered index and many non-clustered indexes
4. A non-clustered index
5. Many non-clustered indexes

Q7. What is OLTP (Online Transaction Processing)?

In OLTP - online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.

  

Q8. What is RDBMS?

Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Inter dependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.

Q9. What are the Properties of the Relational Tables?

Relational tables have the following 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.

Q10. What is Normalization?

Database normalization is a data design and organization process applied to data structures based on rules that help building relational databases. In relational database design, the process of organizing data to minimize redundancy is called normalization. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to 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.

Q11. What is De-normalization?

De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

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Q12. What are the Different Normalization Forms?

1NF: Eliminate Repeating Groups : Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.

2NF: Eliminate Redundant Data: If an attribute depends on only part of a multi-valued key, then remove it to a separate table.

3NF: Eliminate Columns Not Dependent On Key: If attributes do not contribute to a description of the key, then remove them to a separate table. All attributes must be directly dependent on the primary key.

BCNF: Boyce-Codd Normal Form: If there are non-trivial dependencies between candidate key attributes, then 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.

5NF: Isolate Semantically Related Multiple Relationships: There may be practical constrains on information that justify separating logically related many-to-many relationships.

ONF: Optimal Normal Form: A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.

DKNF: Domain-Key Normal Form: A model free from all modification anomalies is said to be in DKNF.

normalization guidelines are always cumulative. For a database to be in 3NF, it must first fulfil all the criteria of a 2NF and 1NF database.

Q13. What are different types of Collation Sensitivity?

1. Case sensitivity - A and a, B and b, etc.
2. Accent sensitivity
3. Kana Sensitivity - When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana sensitive.
4. Width sensitivity - A single-byte character (half-width) and the same character represented as a double-byte character (full-width) are treated differently than it is width sensitive.

Q14. What is the Difference between a Function and a Stored Procedure?

UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section, whereas Stored procedures cannot be. UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables. Inline UDF's can be thought of as views that take parameters and can be used in JOINs and other Rowset operations.

 

Q15. What is subquery? Explain the Properties of a Subquery?

Subqueries are often referred to as sub-selects as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A subquery is executed by enclosing it in a set of parentheses. Subqueries are generally used to return a single row as an atomic value although they may be used to compare values against multiple rows with the IN keyword.

A sub-query is a SELECT statement that is nested within another T-SQL statement. A sub-query SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a result-set. This implies that a sub-query SELECT statement can stand alone, and it does not depend on the statement in which it is nested. A sub-query SELECT statement can return any number of values and can be found in the column list of a SELECT statement, and FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A sub-query can also be used as a parameter to a function call. Basically, a sub-query can be used anywhere an expression can be used.  

Q16. What is User-defined Functions?

User-defined Functions allow defining its own T-SQL functions that can accept zero or more parameters and return a single scalar data value or a table data type.

Q17. What are the types of User-defined Functions that can be created?

Different Types of User-Defined Functions created are as follows:

1. Scalar User-defined Function: A scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages.
2. Inline Table-Value User-defined Function: An Inline table-value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-update-able view of the underlying tables.
3. Multi-Statement Table-Value User-defined Function: A multi-statement table-value user-defined function returns a table, and it is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a T-SQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command, you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior encountered while using a stored procedure which can also return record sets.

Q18. What are Different Types of Join?

1. Cross Join: A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
2. Inner Join: A join that displays only the rows that have a match in both joined tables is known as inner Join. This is the default type of join in the Query and View Designer.
3. Outer Join: A join that includes rows even if they do not have related rows in the joined table is an Outer Join. You can create three different outer join to specify the unmatched rows to be included:

• Left Outer Join: In Left Outer Join, all the rows in the first-named table, i.e. "left" table, which appears leftmost in the JOIN clause, are included. Unmatched rows in the right table do not appear.  
• Right Outer Join: In Right Outer Join, all the rows in the second-named table, i.e. "right" table, which appears rightmost in the JOIN clause are included. Unmatched rows in the left table are not included.
• Full Outer Join: In Full Outer Join, all the rows in all joined tables are included, whether they are matched or not.

Self Join : This is a particular case when one table joins to itself with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company has a hierarchal reporting structure whereby one member of staff reports to another. Self Join can be Outer Join or Inner Join.