So sql, ...count(*)... and ...count(id)... what is the difference?

Question

SQL

In some sql queries they write ...count(*)... and in some ...count(id)... so what's the difference?

Answer 1

SELECT COUNT(*) FROM - iterate over all rows.
SELECT COUNT(id) FROM - iterate over all rows in which the specified field (in this case id ) has a value other than NULL .
What to use is a matter of performance and needs. In the case of primary key , it's more of a performance issue, which will depend on the specific DBMS.