SELECT and Projecting Columns

SELECT Chooses the Columns

SELECT chooses which columns come out of a query. SELECT id, name FROM customers returns just id and name, for every row in customers. SELECT * means every column. Projecting columns never changes how many rows you get.

GOAL

Predict which columns a SELECT list produces, and that the row count is unchanged.

SELECT id, name FROM customers returns how many columns?

CHECK IT

SELECT *
FROM customers

Column SELECT keepsabcNot in the result

customers6 rows · 4/4 cols

id	name	city	referred_by
1	Alice	Tokyo	NULL
2	Bob	Osaka	1
3	Carol	Tokyo	2
4	Dave	Osaka	1
5	Erin	Nagoya	NULL
6	Frank	NULL	3

SELECT chooses which columns come out.