Database and SQL

SQL allows ordering by column aliases defined in the SELECT list, because the alias is resolved after the SELECT clause but before ORDER BY is processed. Hence sorting by an alias is possible, making the claim that it isn’t possible false.

SQL functions are categorized into single-row functions (operate on one row at a time, like UPPER, SUBSTR) and multiple-row functions (operate on groups of rows, like SUM, COUNT, AVG). This classification determines how they're used in queries.

Single‑row functions, such as UPPER or SYSDATE, operate on each row individually and return exactly one value per row. They cannot produce multiple results from a single input row; that behavior belongs to set‑returning functions, making the statement false.

An equi-join is a join based on equality between columns, typically joining on the same column name from different tables. Option B shows Table1.column1 = Table2.column1, which represents an equi-join condition where the same column from both tables is being compared for equality.

The WITH CHECK OPTION clause on a view ensures that any DML operation (INSERT/UPDATE) cannot create rows that the view’s defining query would exclude, protecting against modifications outside the sub‑query’s scope. The other keywords do not provide this restriction.

Explicit DEFAULT values can be specified in both INSERT and UPDATE statements to force a column to use its defined default when the supplied value is omitted or set to DEFAULT. Therefore the option indicating both statements is correct; the others omit one context.

COUNT(DISTINCT expr) counts unique non-null values. Unlike regular COUNT which counts total rows, DISTINCT removes duplicates before counting. NULL values are always excluded from the count.

NVL replaces null values with a specified substitute before aggregation, forcing group functions like SUM or AVG to treat nulls as a concrete value. GROUP BY controls grouping, ORDER BY sorts results, and HAVING filters groups, none of which alter null handling within aggregates.

HAVING filters groups after aggregation, while WHERE filters individual rows before aggregation. You cannot use aggregate functions in WHERE, but you can in HAVING.

Aggregate functions like COUNT, SUM, AVG cannot be used in WHERE clause because WHERE operates on individual rows before grouping. Use HAVING clause to filter on aggregate values.

DELETE with WHERE clause removes only rows matching the condition. It will delete all Employee rows where grade equals 'Y'. If no rows match, nothing is deleted.