The difference between count (1) count (*) count (field) usage in SQL statements

The difference between count (1) count (*) count (field) usage in SQL statements

The Count function is one of the most commonly used functions in SQL statements, and the Count function is a function of the number of records in the statistics table.

A. The difference between count (1) and COUNT (*)

1. The role of Count (1) and COUNT (*):

is to retrieve the number of all record rows in the table, regardless of whether they contain null values.

2. Difference: But count (1) is more efficient than count (*)

Two. The difference between the count (field) and count (1) and COUNT (*)

The function of count (field) is to retrieve the number of non-empty rows of this field in the table, not to count the null record for this field

The difference between count (1) count (*) count (field) usage in SQL statements