SQL Interview Questions & Answers

SQL Interview Questions & Answers


Sql Interview Questions

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  • What Is The Difference Between Sql And Mysql Or Sql Server?

    SQL or Structured Query Language is a language; language that communicates with a relational database thus providing ways of manipulating and creating databases. MySQL and Microsoft’s SQL Server both are relational database management systems that use SQL as their standard relational database language.

  • What Is The Difference Between Sql And Pl/sql?

    PL/SQL is a dialect of SQL that adds procedural features of programming languages in SQL. It was developed by Oracle Corporation in the early 90's to enhance the capabilities of SQL.

  • What Is A Database?

    Database is nothing but an organized form of data for easy access, storing, retrieval and managing of data. This is also known as structured form of data which can be accessed in many ways.
    Example: School Management Database, Bank Management Database.

  • What Are Tables And Fields?

    A table is a set of data that are organized in a model with Columns and Rows. Columns can be categorized as vertical, and Rows are horizontal. A table has specified number of column called fields but can have any number of rows which is called record.
    Example:
    Table: Employee.
    Field: Emp ID, Emp Name, Date of Birth.
    Data: 201478, David, 11/15/1960.
    Can you sort a column using a column alias?
    Yes. A column alias could be used in the ORDER BY clause.

  • What Are The Specific Uses Of Sql Functions?

    SQL functions have the following uses :

    • Performing calculations on data
    • Modifying individual data items
    • Manipulating the output
    • Formatting dates and numbers
    • Converting data types
  • What Are The Case Manipulation Functions Of Sql?

    • LOWER
    • UPPER
    • INITCAP
  • What Are The Types Of Join And Explain Each?

    There are various types of join which can be used to retrieve data and it depends on the relationship between tables.
    Inner join:Inner join return rows when there is at least one match of rows between the tables.
    Right Join:Right join return rows which are common between the tables and all rows of Right hand side table. Simply, it returns all the rows from the right hand side table even though there are no matches in the left hand side table.
    Left Join:Left join return rows which are common between the tables and all rows of Left hand side table. Simply, it returns all the rows from Left hand side table even though there are no matches in the Right hand side table.
    Full Join:Full join return rows when there are matching rows in any one of the tables. This means, it returns all the rows from the left hand side table and all the rows from the right hand side table.

  • What Is Normalization?

    Normalization is the process of minimizing redundancy and dependency by organizing fields and table of a database. The main aim of Normalization is to add, delete or modify field that can be made in a single table.

  • What Is The Purpose Of The Nvl Function?

    The NVL function converts a NULL value to an actual value.

  • What Is The Use Of The Nullif Function?

    The NULLIF function compares two expressions. If they are equal, the function returns null. If they are not equal, the first expression is returned.


  • What Is The Difference Between Cross Joins And Natural Joins?

    The cross join produces the cross product or Cartesian product of two tables. The natural join is based on all the columns having same name and data types in both the tables.

  • What Is The Purpose Of Dml Statements In Sql?

    The DML statements are used to add new rows to a table, update or modify data in existing rows, or remove existing rows from a table.

  • What Are The Types Of Sub Query?

    There are two types of subquery – Correlated and Non-Correlated.
    A correlated subquery cannot be considered as independent query, but it can refer the column in a table listed in the FROM the list of the main query.
    A Non-Correlated sub query can be considered as independent query and the output of subquery are substituted in the main query.

  • What Is A Stored Procedure?

    Stored Procedure is a function consists of many SQL statement to access the database system. Several SQL statements are consolidated into a stored procedure and execute them whenever and wherever required.

  • What Is A Trigger?

    A DB trigger is a code or programs that automatically execute with response to some event on a table or view in a database. Mainly, trigger helps to maintain the integrity of the database.
    Example: When a new student is added to the student database, new records should be created in the related tables like Exam, Score and Attendance tables.

  • What Is The Difference Between Delete And Truncate Commands?

    DELETE command is used to remove rows from the table, and WHERE clause can be used for conditional set of parameters. Commit and Rollback can be performed after delete statement.
    TRUNCATE removes all rows from the table. Truncate operation cannot be rolled back.

  • What Are Local And Global Variables And Their Differences?

    Local variables are the variables which can be used or exist inside the function. They are not known to the other functions and those variables cannot be referred or used. Variables can be created whenever that function is called.
    Global variables are the variables which can be used or exist throughout the program. Same variable declared in global cannot be used in functions. Global variables cannot be created whenever that function is called.

  • What Is A Constraint?

    Constraint can be used to specify the limit on the data type of table. Constraint can be specified while creating or altering the table statement. Sample of constraint are.

    • NOT NULL
    • CHECK
    • DEFAULT
    • UNIQUE
    • PRIMARY KEY
    • FOREIGN KEY
  • What Is Data Integrity?

    Data Integrity defines the accuracy and consistency of data stored in a database. It can also define integrity constraints to enforce business rules on the data when it is entered into the application or database.


  • What Is Auto Increment?

    Auto increment keyword allows the user to create a unique number to be generated when a new record is inserted into the table. AUTO INCREMENT keyword can be used in Oracle and IDENTITY keyword can be used in SQL SERVER.
    Mostly this keyword can be used whenever PRIMARY KEY is used.

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