Computer Dictionary of Information Technology

count

One of the built-in aggregate functions in relational database systems, that returns the number of rows in a result. The argument to the function is nearly always "*", e.g.

  SELECT COUNT(*) FROM books

which returns the number of rows in the "books" table. If, instead, we say

  SELECT COUNT(publisher) FROM books

then only rows with a non-null value in the "publisher" column will be counted.