Which SQL clause is used to remove duplicate rows from a query result?
The DISTINCT keyword filters out duplicate rows, returning only unique combinations of selected columns.
In a relational database, a PRIMARY KEY constraint ensures that:
Primary keys uniquely identify each row and disallow NULL values, providing entity integrity.
Which normal form eliminates partial dependencies on a composite primary key?
Second Normal Form (2NF) requires all non‑key attributes to depend on the entire composite key, not just part of it.
The ANSI SQL data type that stores variable‑length character strings up to a defined limit is:
VARCHAR columns allocate space dynamically for character strings up to the declared length.
Which Oracle background process writes modified database buffers from the SGA to data files?
The DBWn (Database Writer) process flushes dirty buffers to disk to preserve changes.
A FOREIGN KEY constraint enforces:
Referential integrity ensures that every child key value matches an existing parent key or is NULL when allowed.
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What does the acronym DML stand for in SQL?
Data Manipulation Language covers commands that query and modify table data such as SELECT, INSERT, UPDATE, DELETE.
In Oracle, which structure maps logical database blocks to physical file locations?
The extent map in a segment header translates logical blocks to physical disk addresses.
Which command permanently saves all outstanding transactions in an Oracle database?
COMMIT ends the current transaction and makes all changes permanent and visible to other sessions.