Database and SQL

Hibernate does not allow mixing table-per-class hierarchy and table-per-subclass strategies within the same inheritance hierarchy. You must choose one inheritance mapping strategy per hierarchy for consistency and to avoid mapping conflicts.

To make a property read-only from Hibernate's perspective (modifiable only by the database, not through the session), use insert="false" and update="false". This tells Hibernate to include the field in SELECT queries but not in INSERT or UPDATE operations.

When a row might not exist, Session.get() is preferred because it returns null if not found. Session.load() throws an ObjectNotFoundException if the row doesn't exist, and it returns a proxy which can cause issues if the object doesn't actually exist.

In Hibernate, a Bag is an unordered collection that allows duplicate elements, mapped using a java.util.Collection. Unlike a List or an Array, a Bag does not maintain an index column, making the second option correct and the first and third options incorrect.

In Hibernate 3 and later, lazy loading is enabled by default (lazy="true") for collections and associations to optimize application performance and prevent loading unnecessary data from the database. The alternatives like lazy=false are not default settings, and options using 'yes' or 'no' are syntactically invalid.

To achieve the given objective, you can use triggers, which are special PL/SQL programs that are automatically executed in response to specific DML events.

Option A: Auditing the DML operations on the table would provide information about who performed the transactions, but it would not capture the values used in the transactions. Additionally, the auditing information may not be easily transferable to another table for analysis.

Option B: Using an external table would not help in tracking users who performed the transactions and the values used in the transactions. External tables are used to map data in flat files into database tables, or to query data in external sources as if it were in a table. They are not designed for capturing transaction details.

Option C: Using triggers would help you track the users who performed the transactions and the values used in the transactions. You can create a trigger to automatically insert a row into another table, such as an audit table, when a DML operation occurs on the original table. The inserted row can contain information such as the user who performed the transaction, the type of transaction (insert, update, or delete), the date and time of the transaction, and the values used in the transaction. This information can be used for analysis and to detect unauthorized activity.

Option D: Using anonymous PL/SQL blocks would not help in tracking users who performed the transactions and the values used in the transactions. Anonymous PL/SQL blocks are used to execute a sequence of SQL and PL/SQL statements and are not designed for capturing transaction details.

Therefore, the correct option is:

The Answer is: C. By using triggers.

In Oracle SQL, the YY format specifier interprets two-digit years within a sliding window. The year '51' with YY format defaults to 2051 (current century for years 50-99). The RR format uses a different sliding window based on the current year, but YY simply uses the current century boundary.

Oracle's RR format uses a sliding window: if the last two digits of the current year are 00-49, then years 00-49 map to current century and 50-99 map to previous century. Assuming current year context where '51' falls in the 50-99 range, it maps to 1951. This is different from YY which would give 2051.

When the input year is '99', YY and RR formats give different results. YY interprets '99' as 2099 (current century), while RR's sliding window maps '99' to 1999 (previous century, assuming current year is in 00-49 range). Therefore, the outputs are NOT the same.

For year '00', both YY and RR formats resolve to 2000 when the current year is in the 00-49 range. RR's sliding window maps 00-49 to the current century, and YY also maps to current century. Thus, both queries produce the same output.

When '#' is enclosed in single quotes, Oracle treats it as a string literal, not a comment symbol. The query SELECT '#' FROM dual simply returns the character '#' as a string value. No error occurs because it's properly quoted.

When '#' appears without quotes in a SELECT statement, Oracle interprets it as the start of a comment. Since a comment requires valid syntax or continues to end of line, this causes an 'Invalid Character' error. The '#' character is not a valid token outside string literals.

While the first query returns a numeric literal and the second returns a character literal, their standard text output representations are identical in most query tools. Thus, the visual result or output value of both queries is effectively the same.

ROWNUM is a pseudo-column assigned to rows as they are retrieved. In Oracle, ROWNUM values start from 1, and ROWNUM <= 3 will return the first 3 rows. The BETWEEN 0 AND 3 condition effectively filters for ROWNUM <= 3, returning exactly 3 rows from the 30-row table.

ROWNUM conditions have special behavior. ROWNUM IN (1,3) only matches the first row because ROWNUM = 1 is true for the first row, but when checking ROWNUM = 3, the third row never gets ROWNUM = 3 (it fails at 1 or 2). Only the first row satisfies ROWNUM = 1, so exactly 1 row is returned.