SQL Fundamentals & Data Manipulation Flashcards

Which SQL statement is used to permanently save changes made during a transaction?

Answer: COMMIT

COMMIT permanently writes all pending DML changes to the database, making them visible to other sessions.

Which SQL function concatenates two strings in Oracle?

Answer: CONCAT(str1, str2) or str1 || str2

Oracle supports both the CONCAT function and the || pipe operator to join strings together.

What does SELECT * FROM employees WHERE last_name LIKE '_a%'; return?

Answer: Rows where the second character of last_name is 'a'

The underscore (_) wildcard matches exactly one character, so _a% matches any name whose second character is 'a'.

Which aggregate function returns the largest value in a column?

Answer: MAX(column)

MAX(column) is the standard SQL aggregate function that returns the highest value in a group.

A subquery in a WHERE clause that returns exactly one value is called a:

Answer: Single-row subquery

A single-row subquery returns one row and one column, and is used with single-row comparison operators like =, >, <.

Which DML statement is used to change existing data in a table?

Answer: UPDATE

UPDATE is the DML command used to modify existing row values; ALTER is DDL used to change table structure.

What is the effect of adding NOT NULL to a column definition in a CREATE TABLE statement?

Answer: The column cannot store a NULL value; every row must supply a value

NOT NULL is a column-level constraint that forces every inserted or updated row to supply a non-NULL value for that column.