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What is Index?
An index is a physical structure having pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes; they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan occurs when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.
What are aggregate functions? And list the aggregate functions supported by SQL? Aggregate functions are functions that take a collection of values as input and return a one va
Primary Index In primary index, there is a one-to-one relationship among the entries in the index table and the records in the major table. Primary index can be of two types:
What is Data dictionary? A data dictionary is a reserved space in a database that is employed to store information about the database itself. A data dictionary may consist o
Consider the following frequency counts of some itemsets in a transaction database r : freq({A}, r) = 0.405 freq({B}, r) = 0.510 freq({C}, r) = 0.303 freq({A
Define null values. In some cases a certain entity may not have an applicable value for an attribute or if we do not know the value of an attribute for a certain entity. In the
What are the various symbols used to draw an E-R diagram? Explain with the help of an example how weak entity sets are represented in an E-R diagram. Various symbols used to d
Support by Adding Indexes Multiple indexes can be used to access a data file by multiple access paths. In such a scheme only single copy of the data is consider, only the numbe
how design database from begining
Vertical Fragmentation- Vertical fragmentation groups together only those attributes in a relation that are used jointly by various important transactions. A vertical fragment is d
A table joined with itself is called ? A table joined with itself is known as self join table. Normal 0 false false false EN-IN X-NONE X-NONE
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