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Technical Interview Questions and Answers :: SQL

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    What is a PRIMARY KEY?
    Answer:

    The PRIMARY KEY is the column(s) used to uniquely identify each row of a table.

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    12 / 108

    What is a FOREIGN KEY?
    Answer:

    A FOREIGN KEY is one or more columns whose values are based on the PRIMARY or CANDITATE KEY values from the database.

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    13 / 108

    What is a UNIQUE KEY?
    Answer:

    A UNIQUE KEY is one or more columns that must be unique for each row of the table.

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    What is the difference between UNIQUE and PRIMARY KEY?
    Answer:

    The UNIQUE KEY column restricts entry of duplicate values but entry of NULL value is allowed. In case of PRIMARY KEY columns entry of duplicate as well as value is also restricted.

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    Answer:

    A View is a database object that is a logical representation of a table. It is derived from a table but has no storage space of its own and often may be used in the same manner as a table.

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    Answer:

    ROWID is the logical address of a row, and it is unique within the database.

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    Answer:

    INDEX is a general term for an SQL feature used primarily to speed up execution and impose UNIQUENESS upon data. You can use an index to gain fast access to specific information in a database table. An index is a structure that orders the values of one or more columns in a database table. The index provides pointers to the data values stored in specified columns of the table, and then orders those pointers according to the sort order you specify.

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    18 / 108

    The Difference between 'Count' and 'Count (*)'?
    Answer:

    'Count': Counts the number of non-null values. 'Count (*)': Counts the number of rows in the table, including null values and duplicates.

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    19 / 108

    Which are the default databases get installed with the MSSQL installation?
    Answer:

    Master, Model, msdb, Northwind, Pubs, tempdb.

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    20 / 108

    What is the purpose of using COLLATE in a query?
    Answer:

    No Discussion on this question yet!

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