DISTINCT

DISTINCT

Removes duplicate rows from a query result. Example: SELECT DISTINCT major returns each major once.

SELECT DISTINCT syntax

SELECT DISTINCT column_name FROM table_name;

DISTINCT example

SELECT DISTINCT academic_year FROM Students_Spring2024; Returns Freshman, Sophomore, Junior, and Senior once each.

DISTINCT with two columns

Returns unique combinations of all selected fields. Example: SELECT DISTINCT academic_year, major FROM Students_Spring2024;

DISTINCT and multiple columns

If either selected value differs, the row stays. Example: Freshman + Finance and Freshman + Marketing are different rows.

COUNT(DISTINCT column)

Counts unique non-NULL values. Example: SELECT COUNT(DISTINCT major) AS NumMajors FROM Students_Fall2024;

COUNT without DISTINCT

Counts every non-NULL value, including repeats. Example: COUNT(major) counts every student’s major entry.

DISTINCT vs. UNION

DISTINCT removes duplicates within one query result; UNION combines two query results and removes duplicate rows.

When not to use DISTINCT

Do not use it just to hide a bad JOIN; first make sure the JOIN conditions are correct.