Consider tables R(A, B, C) and S(B, D). Then :

"R natural inner join S" contains more tuples than "R natural join S"

"R natural outer join S" contains at least as many tuples as "R natural join S"

"R natural outer join S" contains at least as many tuples as "R natural left outer join S"

"R natural left outer join S" contains at least as many tuples as "R natural right outer join S"

The query "select B, count(distinct C) from R group by B, C count(A) = 1" returns:

Tuple (4, null), (2,1), (null,null)

Consider the query "select A from R T where B in (select C from R where A = T.A)"

The query is equivalent to "select A from R where B=C"

The query returns the empty set

The sub-query (select C from R where A = T.A) is evaluated only once

A program can create several JDBC connections to the same relational database

The JDBC library provides a standard API to access all relational databases

The implementation of the JDBC library is the same for all relational databases

Only the select, insert, update, and delete statements can be executed using JDBC

When a ResultSet object is returned, it is positioned before the first tuple of the set; the first call to next() methiod moves to the first tuple, if it exists.

The executeUpdate() method returns a ResultSet object.

When an SQL query returns the empty set, the corresponding JDBC method returns null

In the getString(int columnIndex) method, the index of the first column is 0, like array indexes in Java.

A transaction commits

When a new transaction is started

When a "rollback" statement is issued

When the user program terminates abnormally

Right after the first SQL statements that executes successfully

the deleteMany() method:

can be used to delete all documents from a collection

returns among other information the number of deleted documents

takes a single parameter, mandatory

returns an error if the specified filter does not match any document

if ordered=false, documents are inserted in an unordered format

if ordered=true, documents are inserted in an unordered format

the insertOne() method:

returns among other information, the value_id of correctly inserted document

allows you to insert multiple documents

returns among other information, the number of correctly inserted documents

the equivalent of following query is: SELECT cust_id, count(*) From orders GROUP BY cust_id HAVING count(*) > 1

db.orders.aggregate( [{_id "$cust_id", count: {$sum: 1}}}, {$match: {count: {$gt: 1}} }])

db.orders.aggregate( [{_id "$cust_id", count: {$sum: 1}}}, {$match: {count: {$gte: 1}} }])

db.orders.aggregate( [{_id "$cust_id", count: {$count: 1}}}, {$match: {count: {$gt: 1}} }])

db.orders.aggregate( [{_id "$cust_id", count: {$count: 1}}}, {$match: {count: {$gte: 1}} }])

the equivalent of the following query is: Select * From people where user_id like "%bc%";

db.people.find({user_id: /bc/})

db.people.find({user_id: {$regex:/bc/}})

db.people.find({user_id: /^bc/})

db.people.find({user_id: {$regex:/^bc/}})

in a $group stage of an aggregate() pipeline

The must be at least one $match

there can be multiple one $match

consider a foreign key from table A to table B with the cascade policy for deletes and updates. Then:

a delete from B can result in a delete from A

an insert into A can result in an insert into B

An update of B can result in a deleted from A

a deleted from A can result in a delete from B

according to CAP theorem, Mongodb has the following properties...

partitionTolerance, consistency

availability, partitionTolerance

availability, partitionTolerance, consistency

BDD_QCM

Authored by Thibaut d'Astorg

Computers

4th Grade

Used 4+ times

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MULTIPLE SELECT QUESTION

45 sec • 1 pt

Null value:

The boolean expression ((A<1) or (A>=1)) always evaluates to true

The boolean expression (A=null) never evaluates to true

The boolean expression (A=null) never evaluates to false

Null can only be used attributes of some numeric type

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Which of the following word pairs are synonims:

table and relation

table and tuple

column and tuple

attribute and row

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Which of the following statements are true regarding the comparison between primary key and unique key ?

A unique key attribute can be null, a primary key attribute cannot

There can be more than one unique key in a table, but there can only be one primary key

A primary key attribute can be null, a unique key attribute cannot

There can be mutliple primary keys in a table, but there can only be one unique key

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Which of the following SQL statements allows you to drop table T ?

drop table T

delete from T

delete from T where true

truncate table T

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Consider table R(A_,B_, C). The query "select A, B from R" returns the same result as:

select distinct A, B from R

select A, B from R where A <> null

select distinct A, B from R where B <> null

select A, B from R where A <> null and B <> null

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Consider the table T (A: int_, B: int). Which query below can produce duplicates?

select * from T

select B from T

select * from T where A = 0

select * from T where B =0

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Consider tables R(A, B) and S(B, C). The query "select A from R natural join S" returns the same result as :

select A from R cross join S

select A from R, S

select A from R, S where R.B = S.B

select A from R cross join S where R.B = S.B

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BDD_QCM

Null value:

Which of the following word pairs are synonims:

Which of the following statements are true regarding the comparison between primary key and unique key ?

Which of the following SQL statements allows you to drop table T ?

Consider table R(A_,B_, C). The query "select A, B from R" returns the same result as:

Consider the table T (A: int_, B: int). Which query below can produce duplicates?

Consider tables R(A, B) and S(B, C). The query "select A from R natural join S" returns the same result as :

Consider tables R(A, B, C) and S(B, D). Then :

The query "select avg(distinct b), min(c) from R" returns:

The query "select count (distinct B), max(distinct B) from R" returns:

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