Learn: Info data study guide

SQL

Structured Query Language; used to retrieve and work with data in databases.

SELECT

Specifies which columns you want to see.

FROM

Specifies which table you are getting data from.

WHERE

Filters individual rows based on a condition.

GROUP BY

Groups rows that have the same value, often used with aggregate functions.

HAVING

Filters groups after GROUP BY; commonly used with AVG, SUM, COUNT, MAX, or MIN.

ORDER BY

Sorts the results.

ASC

Sorts from lowest to highest or A to Z.

DESC

Sorts from highest to lowest or Z to A.

LIMIT

Restricts the number of rows returned.

AVG()

Calculates the average of a column.

SUM()

Adds up the values in a column.

COUNT()

Counts rows or values.

MAX()

Finds the largest/highest value.

MIN()

Finds the smallest/lowest value.

Single quotes

Used around text values and usually date values in SQL.

Text example

'Finance' — text values go inside single quotes.

Date format

'YYYY-MM-DD', such as '2026-10-01'.

WHERE vs HAVING

WHERE filters individual rows; HAVING filters groups/aggregates.

Highest

Usually means ORDER BY column DESC.

Lowest

Usually means ORDER BY column ASC.

Top 3

Usually means ORDER BY ... DESC LIMIT 3.

Bottom 3

Usually means ORDER BY ... ASC LIMIT 3.

"for each department"

Usually means GROUP BY department.

"average salary"

Use AVG(salary).

"total salary"

Use SUM(salary).

"number of employees"

Use COUNT(*).

"highest salary"

Use MAX(salary) or ORDER BY salary DESC depending on what the question asks.

"lowest salary"

Use MIN(salary) or ORDER BY salary ASC depending on what the question asks.