SQL Interview Questions – Set 01

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What is the usage of SQL functions?

Functions are the measured values and cannot create permanent environment changes to SQL server. SQL functions are used for the following purpose:

  • To perform calculations on data
  • To modify individual data items
  • To manipulate the output
  • To format dates and numbers
  • To convert data types

Which function is used to return remainder in a division operator in SQL?

The MOD function returns the remainder in a division operation.

What is the difference between BETWEEN and IN condition operators?

The BETWEEN operator is used to display rows based on a range of values. The values can be numbers, text, and dates as well. BETWEEN operator gives us the count of all the values occurs between a particular range.

The IN condition operator is used to check for values contained in a specific set of values. IN operator is used when we have more than one value to choose.

What is Right Join in SQL?

Right Join is used to retrieve rows which are common between the tables and all rows of a Right-hand side table. It returns all the rows from the right-hand side table even though there are no matches in the left-hand side table.

What is the difference between clustered and non-clustered index in SQL?

There are mainly two type of indexes in SQL, Clustered index and non clustered index. The differences between these two indexes is very important from SQL performance perspective.

  • One table can have only one clustered index, but it can have many non-clustered index. (Approximately 250).
  • A clustered index determines how data is stored physically in the table. Clustered index stores data in the cluster, related data is stored together, so that retrieval of data becomes simple.
  • Clustered indexes store the data information and the data itself whereas non-clustered index stores only the information, and then it will refer you to the data stored in clustered data.
  • Reading from a clustered index is much faster than reading from non-clustered index from the same table.
  • Clustered index sort and store data row in the table or view based on their key value, while non-cluster has a structure separate from the data row.

Does SQL support programming?

SQL refers to the Standard Query Language, which is not actually the programming language. SQL doesn’t have a loop, Conditional statement, logical operations, it can not be used for anything other than data manipulation. It is used like commanding (Query) language to access databases. The primary purpose of SQL is to retrieve, manipulate, update and perform complex operations like joins on the data present in the database.

What is Denormalization in a Database?

Denormalization is used to access the data from higher or lower normal form of database. It also processes redundancy into a table by incorporating data from the related tables. Denormalization adds required redundant term into the tables so that we can avoid using complex joins and many other complex operations. Denormalization doesn?t mean that normalization will not be done, but the denormalization process takes place after the normalization process.

What is a primary key?

A primary key is a field or the combination of fields which uniquely specify a row. The Primary key is a special kind of unique key. Primary key values cannot be NULL. For example, the Social Security Number can be treated as the primary key for any individual.

What is the unique Index?

Unique Index:

For creating a unique index, the user has to check the data in the column because the unique indexes are used when any column of the table has unique values. This indexing does not allow the field to have duplicate values if the column is unique indexed. A unique index can be applied automatically when a primary key is defined.

What are the different types of database management systems?

There are four types of database:

  1. Hierarchical databases (DBMS)
  2. Relational databases (RDBMS)
  3. Network databases (IDMS)

Object-oriented databases RDBMS is one of the most often used databases due to its easy accessibility and supports regarding complex queries.