Jan 31, 2016 · The projection in relational algebra is equivalent to select distinct. In select statement of sql, duplicates are allowed as it is based on multiset theory but in projection of relational algebra, which is based on set theory, duplicates are not allowed.

Oct 29, 2012 · The commas in the FROM clause of an SQL expression represent the cross product. So the equivalent relational algebra expression is: π a1,a2,a3...an (σ P (R1 x R2 x ... x Rm))

I need to count the number of DISTINCT hotels every user has reviewed using RELATIONAL ALGEBRA only. How can I do that? example to show notations I use: R = ƔUser,COUNT(Hotel_reviewed)->Num_Reviews (InitialRelation- table 1) would give the number of reviews by each user . The result should be the following table: example to show notations I …

Translating an arbitrary SQL query into a logical query plan (i.e., a rela-tional algebra expression) is a complex task. In these course notes we try to explain the most important elements of this translation by making the following simplifying assumptions:

Consider the following SQL query. Select distinct $a_1, a_2, …, a_n$ from $r_1, r_2, …, r_m$ where P. For an arbitrary predicate P, this query is equivalent to which of the following relational algebra expressions? $\Pi_{a_1, a_2, … a_n} \sigma_p \left(r_1 \times r_2 …

To remove duplicates from our result, we can use the SQL keyword DISTINCT. In terms of relational algebra, we use a selection ( ), to lter rows with the appropriate predicate, and a projection ( ) to get the desired columns.

Sep 30, 2015 · How can i represent Statement 3 in terms of SQL in the same way as it is in Relation Algebra (i.e without using any operator other than minus/Except(-) and Cross join(*)). I am trying to achieve it without the use of NOT EXISTS and EXISTS condition. Schema of tables is as follows: Sailors(sid: integer, sname: string, rating: integer, age: real)

Iterate over PRODUCT... ...join with PURCHASE... ...join with CUSTOMER... ...select tuples with Price>100 and City=‘Seattle’... ...eliminate duplicates... ...and that’s the final answer ! Sets: {a,b,c}, {a,d,e,f}, { }, . . . Bags: {a, a, b, c}, {b, b, b, b, b}, . . . What do they mean over bags ? What about Intersection ? Answer(N, S)

Relational algebra expressions are procedural. SELECT. Which of the two equivalent expressions is more easily evaluated? Tuple variables are essential in this query! SELECT DISTINCT ..... FROM ..... WHERE S.Name || ‘--’ || S. Address = ....

Example: To compute the relational algebra expression πA 1,...,An(R) in SQL, use SELECT DISTINCT A1,...,An FROM R. Some SQL operators, like UNION, INTERSECT, and EXCEPT, automatically perform duplicate elimination. If we always used DISTINCT etc., the semantics of SQL would match relational algebra. However, when efficiency is an issue this is ...