Managing Databases with Oracle Questions and Answers

Answer: A

Correct answer: True

START filename, and its abbreviation @filename, reads the file and executes the statements in it one after another as though they had been typed. This is how scripts are run, and the assumed .sql extension means the name is usually given without one.

Answer: A

Correct answer: True

DESCRIBE, commonly abbreviated to DESC, lists a table’s columns with their data types and whether each accepts nulls. It reports the definition only and returns none of the stored rows.

Answer: A

Correct answer: True

Oracle runs on Unix, Linux, Windows and mainframe platforms alike, and it has long led the market for enterprise relational database systems. The claim is a general one about the product’s reach rather than a technical point, and the portability is the part that matters to a developer: the same SQL and PL/SQL run on any of those platforms.

Answer: D

Correct answer: LIST.

LIST, or L, displays the contents of the SQL buffer with the lines numbered, so that a particular line can be selected and changed before the statement is re-run with a slash. It is part of the small line-editing facility SQL*Plus provides for correcting a statement without retyping it.

Answer: B

Correct answer: False

It is the forward slash that executes the buffer, not a backslash, and typing a backslash achieves nothing. The distinction matters in practice because the slash is how a statement is re-run after being corrected, and how a PL/SQL block is submitted - a semicolon cannot end such a block, since its body is full of semicolons already.

Answer: B

Correct answer: Instance Failure

Instance failure is the loss of the Oracle instance itself - the memory structures and background processes - through an operating system crash, a hardware fault or a power loss. The datafiles are undamaged, so recovery is automatic on the next startup: Oracle rolls forward the redo log and rolls back uncommitted transactions. Media failure, by contrast, means the files themselves are damaged and needs a restore.

Answer: B

Correct answer: DURING

Oracle triggers fire BEFORE or AFTER the triggering statement, or INSTEAD OF it, the last being used on views that are not otherwise updatable. There is no DURING option, and there could not usefully be one, since the statement is atomic from the trigger’s point of view.

Answer: A

Correct answer: True

A semicolon at the end of a line terminates the statement and submits it for execution in one action, which is the ordinary way of running a single SQL statement. The alternative is a slash on a line of its own, which executes whatever is already in the buffer and is needed for PL/SQL blocks.

Answer: A

Correct answer: True

SQL*Plus assumes the extension .sql when a file name is given without one, so a script saved as build.sql is run simply as @build. The convention is worth following, since a file with any other extension has to be named in full every time it is used.

Answer: B

Correct answer: ON UPDATE CASCADE

Oracle supports ON DELETE CASCADE but not ON UPDATE CASCADE, so a change to a parent key value cannot be propagated automatically to the children; it must be done with a trigger or, better, avoided by using a surrogate key that never changes. The two sequence commands are both supported.