SQL Basics Flashcards

Question 1

SQL: basic query structure?

Accepted Answer

SELECT columns FROM table WHERE condition

Question 2

SQL: difference between INNER JOIN and LEFT JOIN?

Accepted Answer

INNER returns only matching rows; LEFT keeps all left-table rows with NULLs for non-matches

Question 3

SQL: filter grouped results?

Accepted Answer

HAVING (WHERE filters rows before grouping)

Question 4

SQL: count rows per category?

Accepted Answer

SELECT category, COUNT(*) FROM t GROUP BY category

Question 5

SQL: sort results descending?

Accepted Answer

ORDER BY column DESC

Question 6

SQL: what does DISTINCT do?

Accepted Answer

Removes duplicate rows from the result

Question 7

SQL: pattern-match a string?

Accepted Answer

WHERE name LIKE 'A%' (% is any sequence, _ is one character)

Question 8

SQL: what is a primary key?

Accepted Answer

A column (or set) that uniquely identifies each row

Question 9

SQL: return at most 10 rows?

Accepted Answer

LIMIT 10

Question 10

SQL: what does NULL = NULL evaluate to?

Accepted Answer

NULL (unknown) — use IS NULL to test for nulls

Free SQL Basics Flashcards