What does COUNT(l.loan_id) AS loan_count mean in an SQL query?

COUNT(l.loan_id) AS loan_count in SQL is an aggregate function that counts the number of non-null (not NULL) values in the loan_id column of the table or alias l. The result of the count will be displayed in the final dataset under the name loan_count.

For example, if there are 10 rows in the sample, and in 7 of them loan_id is not NULL, then loan_count will be 7. This is often used to count the number of related records, such as the number of loans a client has.