MC Which statement is NOT CORRECT? The number of block accesses determines the performance, not the number of rows retrieved. incorrect For range queries, a primary or clustered index is more efficient than a secondary index. incorrect The more attribute types are included in the index, the higher the performance impact is on update queries. incorrect The more selective a query predicate's FF, the less desirable it is to use the index on the corresponding attribute type in the access plan. correct
MC Given 2 tables R and S. Which of the following join strategies is described by the following algorithm:
denote S -> outer table
for every row s in S do {
for every row r in R do {
if r(a) = s(b) then join r with s and place in output buffer
}
} Hash join incorrect Sort-Merge join incorrect Nested loop join correct None of these joins incorrect
MC Which statement is NOT CORRECT? An index can be used to create a physical ordering of rows. incorrect Index creation can help improve the performance of join queries. incorrect Indexing makes it harder to enforce uniqueness on a (combination of) column(s). correct An index implies a logical ordering of the rows in a table. incorrect
MC Which statement is NOT CORRECT? 'Network attach' refers to establishing a many-to-many connection between storage devices and the corresponding servers by means of network technology. incorrect Although SCSI has been a popular medium for connecting storage devices to servers and/or processors in the past, nowadays, it is not used anymore for high performance and high capacity workstations and servers. correct The management of data storage is more expensive than the purchase of storage hardware, which is why businesses opt for enterprise storage subsystems. incorrect The SCSI I/O command set is a type of block-level I/O protocol which can be exchanged over SCSI, Ethernet or Fibre Channel cabling. incorrect
MC Which statement is NOT CORRECT? The more selective a query predicate's FF, the less desirable it is to use the index on the corresponding attribute type in the access plan. correct The more attribute types are included in the index, the higher the performance impact is on update queries. incorrect For range queries, a primary or clustered index is more efficient than a secondary index. incorrect The number of block accesses determines the performance, not the number of rows retrieved. incorrect
MC Which statement is NOT CORRECT? Indexing makes it harder to enforce uniqueness on a (combination of) column(s). correct An index implies a logical ordering of the rows in a table. incorrect Index creation can help improve the performance of join queries. incorrect An index can be used to create a physical ordering of rows. incorrect
MC Which statement is CORRECT? The only points of failure of a database system are the availability of database functionality and the availability of the data itself. incorrect The filter factor of a predicate is the fraction of rows that contain a missing value for that predicate. incorrect An index implies a logical ordering of the rows in a table. correct Current versions of SQL require a specific internal data model. incorrect
MC Which statement is NOT CORRECT? Using error correcting codes for fault tolerance requires extra storage space, almost as much as when opting for disk mirroring. correct It is often more efficient to combine multiple smaller physical disk drives into one larger logical drive because reliability can be improved by introducing some measure of data redundancy. incorrect It is often more efficient to combine multiple smaller physical disk drives into one larger logical drive because having multiple physical drives allows for parallel retrieval, which results in much more improved performance. incorrect With bit level data striping, every disk participates in each read or write operation. incorrect
MC Which statement is CORRECT? Table cardinality is another way of referring to the number of columns in a table. incorrect If no further statistical information about a predicate is available, the filter factor of that predicate can be estimated by dividing 1 by the number of different values the attribute type can have. correct The filter factor of a predicate is the fraction of rows that contain a missing value for that predicate. incorrect SQL is a declarative language, meaning that the programmer has to specify what data to retrieve and how the data is to be located and retrieved from the physical database files. incorrect
MC Which statement is NOT CORRECT? Although SCSI has been a popular medium for connecting storage devices to servers and/or processors in the past, nowadays, it is not used anymore for high performance and high capacity workstations and servers. correct It is often more efficient to combine multiple smaller physical disk drives into one larger logical drive because reliability can be improved by introducing some measure of data redundancy. incorrect The number of block accesses determines the performance, not the number of rows retrieved. incorrect If no further statistical information about a predicate is available, the filter factor of that predicate can be estimated by dividing 1 by the number of different values the attribute type can have. incorrect