SQL Fundamentals & Data Manipulation Flashcards

Which UPDATE statement correctly increases every employee's salary by 10%?

Answer: UPDATE employees SET salary = salary * 1.10;

UPDATE uses SET clause with assignment; multiplying by 1.10 adds 10% to the existing value.

What happens when you execute DELETE FROM orders; with no WHERE clause?

Answer: All rows in the orders table are deleted but the table structure remains

DELETE without WHERE removes all rows while leaving the table structure, indexes, and constraints intact.

Which SQL clause filters rows AFTER a GROUP BY aggregation has been applied?

Answer: HAVING

HAVING filters the result of grouped rows, whereas WHERE filters individual rows before grouping.

A UNIQUE constraint on a column differs from a PRIMARY KEY constraint because a UNIQUE column:

Answer: Allows NULL values

A UNIQUE constraint permits NULL (multiple NULLs are allowed in Oracle), whereas PRIMARY KEY prohibits NULLs.

Which function returns the number of non-NULL values in a column?

Answer: COUNT(column)

COUNT(column) counts only non-NULL values in that column, while COUNT(*) counts all rows including NULLs.

In a SELECT statement, what is the correct order of these clauses: WHERE, FROM, SELECT, ORDER BY?

Answer: SELECT, FROM, WHERE, ORDER BY

Standard SQL clause order is SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY.

Which INSERT syntax adds multiple rows in a single statement using Oracle's multi-table insert shorthand for a single table?

Answer: INSERT ALL INTO emp VALUES(...) INTO emp VALUES(...) SELECT 1 FROM dual;

Oracle's INSERT ALL ... SELECT 1 FROM DUAL syntax inserts multiple rows in one DML statement.