The meaning of COUNT(1)?
I am puzzled as to what the meaning of COUNT(1) is? It counts the first column or a column named 1?
I just avoid it by using
COUNT(period_id) in this video
Steven Parker180,244 Points
COUNT" function counts every row for which the supplied value is not null. So there's no difference between providing a "*", a literal digit, or an ID field. The number "1" is just a common convention used used to mean "count all rows".
But if you supply a field name that can contain nulls, rows where that field is null will not be counted. For examples, using the playground from this video:
SELECT COUNT(1) FROM subjects; /* 24 (all rows) */ SELECT COUNT(name) FROM subjects; /* 24 (no nulls) */ SELECT COUNT(grade) FROM subjects; /* 18 (because of nulls) */
Tommy Gebru29,647 Points
I also keep assuming it to be either the first column of the table or the first parameter of the SELECT statement