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Explain the difference between using functions along with and without grouping attributes in relational algebra. Give examples.
Ans: Group functions are used to group data of similar type. GAMMA = grouping and aggregation Applying GAMMAL(R)• Group R according to all the grouping attributes on list L.1. That is: form one group for each distinct list of values for those attributes in R.• Within each group, compute AGG(A ) for each aggregation on list L.• Result has one tuple for each group:1. The grouping attributes and2. Their group's aggregations. Example: Grouping /Aggregation R = ( A B C ) 1 2 3 4 5 6 1 2 5 GAMMAA,B,AVG(C) (R) = ? First, group R by A and B : A B C 1 2 3 1 2 5 4 5 6 Then, average C within groups: A B AVG(C) 1 2 4 4 5 6
Why are cursors necessary in embedded SQL? A cursor is an object used to store the output of a query for row-by-row processing through the application programs. SQL statements
A file of employee have 10,000 blocks on a cylinder of a disk with characteristics r=8ms and btt=0.6ms I want to know the cost of read inthe file under following conditions for a q
Ask questiwhat is row indicator in database on #Minimum 100 words accepted#
Express types of information available in MySQL? Information as regards the result of queries: This includes number of records affected by any SELECT or UPDATE or DELETE st
What are the Requirements of algorithm designer Algorithm designer should: i) Select proper algorithm so as to minimize implementation cost ii) Find most appropriate d
What are uncommitted modifications? The immediate-modification technique permits database modifications to be output to the database whereas the transaction is still in the act
The PROJECT operation The project operation is used to choose the records with specified attributes as discarding the others based on some related criteria. This is denotes as ∏
What is completeness constraint on generalization? Define the variation between total and partial design constraint. Give an example each. Ans: Completeness Constraints
object oriented database
Using Literal Character String Example: To print IS A as one string with column name employee SELECT ENAME || ' IS A ' || JOB AS "EMPLOYEE" FROM EMP;
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