DB Bitmap Index قواعد بيانات متقدمة لأول مرة على اليتيوب العربي.

تم عمل مدونة بتمنى منكم زيارتها ومشاركتها لكي يتم تفعيلها وان شاء الله سأقوم بشرح كامل على كيفية عمل مدونة وكيفية الربح منها بعد نجاح هذه المدونة سأقوم بشرح التجربة كاملة ان شاء الله
https://technologycom20.blogspot.com/ لاول مرة على اليتيوب العربي :

شرح بالعربي DB Bitmap
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المطور /زكريا الخميسي
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Bitmap Indexing in DBMSBitmap
Indexing is a special type of database indexing that uses bitmaps. This technique is used for huge databases, when column is of low cardinality and these columns are most frequently used in the query.Need of Bitmap Indexing –The need of Bitmap Indexing will be clear through the below given example :For example, Let us say that a company holds an employee table with entries like EmpNo, EmpName, Job, New_Emp and salary. Let us assume that the employees are hired once in the year, therefore the table will be updated very less and will remain static most of the time. But the columns will be frequently used in queries to retrieve data like : No. of female employees in the company etc. In this case we need a file organization method which should be fast enough to give quick results. But any of the traditional file organization method is not that fast, therefore we switch to a better method of storing and retrieving data known as Bitmap Indexing.How Bitmap Indexing is done –In the above example of table employee, we can see that the column New_Emp has only two values Yes and No based upon the fact that the employee is new to the company or not. Similarily let us assume that the Job of the Employees is divided into 4 categories only i.e Manager, Analyst, Clerk and Salesman. Such columns are called columns with low cardinality. Even though these columns have less unique values, they can be queried very often.Bit: Bit is a basic unit of information used in computing that can have only one of two values either 0 or 1 . The two values of a binary digit can also be interpreted as logical values true/false or yes/no.In Bitmap Indexing these bits are used to represent the unique values in those low cardinality columns. This technique of storing the low cardinality rows in form of bits are called bitmap indices
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