[Q.71] Which SQL aggregate function counts the number of non-NULL values in a column?
COUNT(column_name) evaluates non-NULL entries in the specified attribute.
[Q.72] In SQL, which clause is used to filter group results after applying an aggregate function?
WHERE filters individual rows prior to grouping; HAVING filters groups after aggregation.
[Q.73] A database transaction log file (WAL - Write-Ahead Logging) ensures which ACID property?
Write-Ahead Logging records transaction changes to non-volatile disk log before writing to database, ensuring Durability.
[Q.74] In ER modeling, a Multi-Valued Attribute is represented by a:
Double ellipses symbolize multi-valued attributes (e.g. Phone Numbers).
[Q.75] What is the result of the relational operation R MINUS S?
Difference R - S returns tuples belonging exclusively to relation R.