Câu hỏi gốc môn DBI202

524 câu gốc, sắp theo số đề từng chứa câu đó.

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What is the value of the query: ```sql SELECT 1 + NULL + 2 ``` when evaluated on Microsoft SQL Server?

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When designing a database you should ____.

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Suppose relations: $R(A,B)$ and $S(B,C,D)$ (see figure). | R | | | :--- | :--- | | A | B | | 1 | 2 | | 3 | 4 | | 5 | 6 | | S | | | | :--- | :--- | :--- | | B | C | D | | 2 | 4 | 6 | | 4 | 6 | 8 | | 4 | 7 | 9 | Compute the full outer join of $R$ and $S$, where the condition is: $R.A > S.B$ AND $R.B = S.C$. Which of the following tuples of $R$ or $S$ is dangling (and therefore needs to be padded in the outer-join)?

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Relation $R(x,y)$ currently consists of only one tuple $(\mathrm{NULL},\mathrm{NULL})$. Which of the following queries will produce a nonempty output? That is, at least one tuple will be produced, although the tuple(s) may have NULLs.

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A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable). What does "Isolated" mean?

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What is the condition that a relation schema $R$ is in BCNF (Boyce-Codd Normal Form)?

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Choose a correct statement.

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What type of relationship is expressed with the phrase "Students take Classes"?

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Suppose relations: R(A,B) and S(B,C,D) (see figure). Compute the R right outer join S, where the condition is: R.B = S.B. Then identify two tuples of R that do not appear in the computed result. | R | | S | | | | |---|---|---|---|---|---| | A | B | B | C | D | | | 1 | a | a | 4 | 6 | | | 3 | b | c | 6 | 8 | | | 5 | c | c | 5 | 5 | | | 7 | d | c | 7 | 9 | |

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Look at the following statements: (a) We should pick the right kind of elements (b) When an entity has no non-primary key attribute, we should convert that entity to an attribute (c) Use weak entities when-ever possible (d) Always make redundancies

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Which statements about a lock in DBMS are true? a) Granularity: the size of the lock b) Granularity: the type of the lock c) Mode: the type of the lock d) Duration: the time in seconds that the DBMS waits for a lock to be released

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When is a set of functional dependencies $F$ said to be minimal? a) Every dependency in $F$ has a single attribute for its right-hand side. b) We cannot replace any dependency $X \to A$ in $F$ with other dependency $Y \to A$, where $Y$ is a proper subset of $X$, and the changed set of dependencies is still equivalent to $F$. c) We cannot remove any dependency from $F$ and still have a set of dependencies that is equivalent to $F$. d) Every dependency in $F$ has more attributes for its right-hand side.

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What is another term for a row in a relational table?

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Given the relation $R(A,B,C,D,E)$ with the following FDs: $D \to C$, $CE \to A$, $D \to A$, and $AE \to D$. Which of the following attribute sets is a key?

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Today, the two important data models are:

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Give a relation $R(A,B,C,D)$ like this: | A | B | C | D | | :--- | :--- | :--- | :--- | | 1 | 2 | 3 | 6 | | 1 | 3 | 3 | 6 | | 2 | 4 | 5 | 7 | Please choose the incorrect functional dependency:

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Suppose we have a relation R(A, B, C, D, E, F) with the following set of FDs: A->C DE-> F B->D Which is the KEY of R?

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What is a key attribute in a relation?

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To update a relation's schema, which one of the following statements can be used?

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Suppose relation $R(A, B, C)$ has the following tuples: | A | B | C | | :--- | :--- | :--- | | 1 | 1 | 3 | | 1 | 2 | 3 | | 2 | 1 | 4 | | 2 | 3 | 5 | | 2 | 4 | 1 | | 3 | 2 | 4 | | 3 | 3 | 6 | Which tuple is contained in the result of the following query: ```sql SELECT A, COUNT(DISTINCT B) FROM R GROUP BY A HAVING SUM(B) > 3; ```

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Câu hỏi gốc môn DBI202

What is the value of the query: ```sql SELECT 1 + NULL + 2 ``` when evaluated on Microsoft SQL Server?

When designing a database you should ____.

Relation $R(x,y)$ currently consists of only one tuple $(\mathrm{NULL},\mathrm{NULL})$. Which of the following queries will produce a nonempty output? That is, at least one tuple will be produced, although the tuple(s) may have NULLs.

A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable). What does "Isolated" mean?

What is the condition that a relation schema $R$ is in BCNF (Boyce-Codd Normal Form)?

Choose a correct statement.

What type of relationship is expressed with the phrase "Students take Classes"?

Look at the following statements: (a) We should pick the right kind of elements (b) When an entity has no non-primary key attribute, we should convert that entity to an attribute (c) Use weak entities when-ever possible (d) Always make redundancies

Which statements about a lock in DBMS are true? a) Granularity: the size of the lock b) Granularity: the type of the lock c) Mode: the type of the lock d) Duration: the time in seconds that the DBMS waits for a lock to be released

What is another term for a row in a relational table?

Given the relation $R(A,B,C,D,E)$ with the following FDs: $D \to C$, $CE \to A$, $D \to A$, and $AE \to D$. Which of the following attribute sets is a key?

Today, the two important data models are:

Give a relation $R(A,B,C,D)$ like this: | A | B | C | D | | :--- | :--- | :--- | :--- | | 1 | 2 | 3 | 6 | | 1 | 3 | 3 | 6 | | 2 | 4 | 5 | 7 | Please choose the incorrect functional dependency:

Suppose we have a relation R(A, B, C, D, E, F) with the following set of FDs: A->C DE-> F B->D Which is the KEY of R?

What is a key attribute in a relation?

To update a relation's schema, which one of the following statements can be used?