SQL Fundamentals

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.

NULL represents unknown or missing data, not zero or blank. Zero is a numeric value and blank space is a character, but NULL means no value exists at all.

ROUND function rounds to specified decimal places. ROUND(1111.93412, 3) keeps 3 decimal places, so 1111.93412 becomes 1111.934 - the fourth decimal (1) is dropped, not rounded up because it's less than 5.

MOD function returns the remainder when dividing two values. For example, MOD(10, 3) returns 1 because 10 divided by 3 is 3 with remainder 1. Option A describes QUOTIENT or division, not MOD.

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).

Multiple-row operators in SQL are IN, ANY, ALL, EXISTS, and their negations (NOT IN, etc.). OF is not a valid SQL operator - it's not listed among single-row operators (=, !=, <, >, <=, >=) or multiple-row operators. Option A (IN), C (ALL), and D (ANY) are all valid multiple-row operators.

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 (...)'.

In Oracle SQL, SYSDATE function returns the current system date and time. Option A (Date) is a data type, not a function. Options C (Current Date) and D (System Date) are not valid SQL functions. SYSDATE is the correct function to get current date.

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.

In SQL, character comparisons are case-sensitive by default, meaning 'A' is different from 'a'. String literals in WHERE conditions match exactly including case unless explicitly modified.

SQL follows three-valued logic (true, false, null). Any arithmetic expression with a NULL operand evaluates to NULL, not a numeric result. NULL represents unknown or missing values.

The double pipe (||) is the standard SQL concatenation operator that joins two strings together. The other symbols are arithmetic operators (+ addition, - subtraction, * multiplication).

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

SELECT * from EMP; is the correct SQL syntax to select all columns. The asterisk (*) wildcard represents all columns in the table.

This statement will fail due to syntax errors: there are extra spaces (select, ename, emp) and the string literal Scott is not properly quoted with single quotes. SQL requires single quotes for string literals.