Technical Interview Questions and Answers :: SQL
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The PRIMARY KEY is the column(s) used to uniquely identify each row of a table.
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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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A UNIQUE KEY is one or more columns that must be unique for each row of the table.
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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
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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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ROWID is the logical address of a row, and it is unique within the database.
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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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'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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Master, Model, msdb, Northwind, Pubs, tempdb.
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