Recent questions tagged joins - GATE CSE Doubts

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Joins in Relational Algebra (Self Doubt) while reading Elmasri Navathe

asked Jan 10 in Databases by shubhojit1412 (5 points) | 15 views

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Self Doubt (Nested Loop Join)
Can someone please clarify why we keep the smaller loop outer and the bigger loop inner? (i.e. why do we select the relation with smaller number of tuples as the outer relation)

asked Aug 16, 2020 in Databases by Mellophi (363 points) | 30 views

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GATE2012-50 Video Solution
Consider the following relations $A, B$ and $C:$ ... is the same as that of $A$. $(A\cup B)\bowtie _{A.Id > 40 \vee C.Id < 15} C$ $7$ $4$ $5$ $9$

asked Apr 18, 2020 in Databases by admin (569 points) | 9 views

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GATE2004-14 Video Solution
Consider the following relation schema pertaining to a students database: Students (rollno, name, address) Enroll (rollno, courseno, coursename) where the primary keys are shown underlined. The number of tuples in the student and Enroll tables are $120$ and $8$ respectively. What ... (Student * Enroll), where *' denotes natural join? $8, 8$ $120, 8$ $960, 8$ $960, 120$

asked Apr 18, 2020 in Databases by admin (569 points) | 20 views

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GATE2014-2-30 Video Solution
Consider a join (relation algebra) between relations $r(R)$ and $s(S)$ using the nested loop method. There are 3 buffers each of size equal to disk block size, out of which one buffer is reserved for intermediate results. Assuming size(r(R))<size(s(S)) , the join ... $s(S)$ is more than 0.5. join selection factor between $r(R)$ and $s(S)$ is less than 0.5.

asked Apr 18, 2020 in Databases by admin (569 points) | 10 views

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GATE2005-IT-82b Video Solution
A database table $T_1$ has $2000$ records and occupies $80$ disk blocks. Another table $T_2$ has $400$ records and occupies $20$ disk blocks. These two tables have to be joined as per a specified join condition that needs to be evaluated for ... outer loop, the reduction in number of block accesses required for reading the data will be $0$ $30400$ $38400$ $798400$

asked Apr 18, 2020 in Databases by admin (569 points) | 11 views

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GATE2007-IT-68 Video Solution
Consider the following relation schemas : b-Schema = (b-name, b-city, assets) a-Schema = (a-num, b-name, bal) d-Schema = (c-name, a-number) Let branch, account and depositor be respectively instances of the above schemas. Assume that account and ... depositor) Пc-name (σb-city = "Agra" branch ⋈ (σb-city = "Agra" ⋀ bal < 0 account ⋈ depositor))

asked Apr 18, 2020 in Databases by admin (569 points) | 12 views

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GATE2006-IT-14 Video Solution
Consider the relations r1(P, Q, R) and r2(R, S, T) with primary keys P and R respectively. The relation r1 contains 2000 tuples and r2 contains 2500 tuples. The maximum size of the join r1⋈ r2 is : 2000 2500 4500 5000

asked Apr 18, 2020 in Databases by admin (569 points) | 7 views

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GATE2005-IT-82a Video Solution
A database table $T_1$ has $2000$ records and occupies $80$ disk blocks. Another table $T_2$ has $400$ records and occupies $20$ disk blocks. These two tables have to be joined as per a specified join condition that needs to be evaluated for every ... be used in outer loop, the number of block accesses required for reading the data are $800000$ $40080$ $32020$ $100$

asked Apr 18, 2020 in Databases by admin (569 points) | 11 views

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Self Doubt - Nested Loop Join (No. of Seeks)
What do you mean by Seek? For Natural Loop Join, we calculate No. of Seeks are (nr + br). Assume that, Relation r is called the Outer Relation and Relation s is called the Inner Relation. (ni,bj) – ni represents total no. of tuples and bj represents no. of blocks in that relation. Reference (Korth) – For Block Nested-Loop Join –

asked Sep 10, 2019 in Databases by ayushsomani (-1 points) | 33 views

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Doubts Regarding join algorithm
What is the number of block access in Indexed Nested Loop join & Sort-merge Join??? given, No. of blocks in relation R = $B_{r}$ No. of blocks in relation S = $B_{s}$ No. of records in relation i = $r_{i}$ Join is like R x S & size of R is less than size of S

asked Jul 10, 2019 in Databases by mrinmoyh (23 points) | 12 views

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