Database and SQL

SQL functions are broadly categorized into single-row functions, which operate on single rows and return one result per row, and multiple-row (or group/aggregate) functions, which operate on sets of rows to return a single result. Double-row or two-row functions do not exist.

Single-row functions (like UPPER, SUBSTR, ROUND) return exactly one result per input row processed. The statement claims they can return multiple results per row, which is incorrect - that would describe aggregate functions or group functions.

Outer joins (LEFT, RIGHT, FULL) are specifically designed to return unmatched rows from one or both tables, along with matched rows. This is their defining purpose - unlike inner joins which only return matches. Option A correctly identifies this behavior.

In Oracle SQL syntax, the (+) operator is placed next to the column that may be null to indicate an outer join. For example, 'WHERE table1.id = table2.id(+)' creates a right outer join. This is Oracle's legacy outer join syntax.

A self-join joins a table to itself, typically using table aliases to treat it as two separate copies. This is used for hierarchical data (employee-manager) or comparing rows within the same table. Option A correctly names this join type.

DISTINCT keyword in SELECT statement removes duplicate rows from the result set, returning only unique values. Options A, C, and D are not valid SQL keywords for eliminating duplicates.

Subqueries are classified as single-row (return one row) or multiple-row (return multiple rows). This classification determines which operators you can use: single-row operators (=, >, <) vs multiple-row operators (IN, ANY, ALL). Option D is correct despite slightly awkward phrasing.

A single-row subquery returns exactly one row from the inner query, allowing use of single-row comparison operators like =, >, <, >=, <=, !=. If it returns zero or multiple rows, these operators will cause an error.

The subquery uses GROUP BY Rollnum, which returns one row per unique Rollnum (multiple rows total). The outer query uses = (single-row operator), which cannot handle multiple results. This triggers the error 'single-row subquery returns more than one row'. Note: GROUPBY should be GROUP BY (missing space).

ALL operator compares a value to EVERY value returned by a subquery. For example, salary > ALL (subquery) means salary is greater than the maximum value in the subquery. ANY compares to at least one value, IN checks for membership, and OF is not a valid operator.

DML (Data Manipulation Language) includes INSERT (add new rows), UPDATE (modify existing rows), and DELETE (remove existing rows). All three actions are DML operations, so 'All of the above' is correct.

Correct INSERT syntax is INSERT INTO tablename VALUES (...). Option A has 'Insert to' instead of 'Insert into'. Option B is missing the VALUES keyword. Option C is correct: INSERT INTO tablename VALUES (...). Note: Option C says 'Insert into table tablename' which has an extra 'table' - the standard is just 'INSERT INTO tablename VALUES (...)'.

The WHERE clause filters rows based on specified conditions, returning only those rows that satisfy the criteria. DISTINCT removes duplicate rows, while projection refers to selecting specific columns in a SELECT statement.

SQL SELECT supports projection (choosing columns), selection (filtering rows with WHERE), and join (combining tables). All three capabilities are fundamental to SELECT statements.