May 16, 2021 SQL
The COUNT() function returns the number of rows that match the specified criteria.
The COUNT (column_name) function returns the number of values for the specified column (NULL does not count):
SELECT COUNT(column_name) FROM table_name;
The COUNT function returns the number of records in the table:
SELECT COUNT(*) FROM table_name;
The COUNT (DISTINCT column_name) function returns the number of different values for the specified column:
SELECT COUNT(DISTINCT column_name) FROM table_name;
Note: COUNT (DISTINCT) is available for ORACLE and Microsoft SQL Server, but not for Microsoft Access.
In this tutorial, we'll use the RUNOOB sample database.
Here's the data access_log the "Here's the table":
+-----+---------+-------+------------+
| aid | site_id | count | date |
+-----+---------+-------+------------+
| 1 | 1 | 45 | 2016-05-10 |
| 2 | 3 | 100 | 2016-05-13 |
| 3 | 1 | 230 | 2016-05-14 |
| 4 | 2 | 10 | 2016-05-14 |
| 5 | 5 | 205 | 2016-05-14 |
| 6 | 4 | 13 | 2016-05-15 |
| 7 | 3 | 220 | 2016-05-15 |
| 8 | 5 | 545 | 2016-05-16 |
| 9 | 3 | 201 | 2016-05-17 |
+-----+---------+-------+------------+
The following SQL statement calculates access_log total access in the "site_id" table, "
SELECT COUNT(count) AS nums FROM access_log
WHERE site_id=3;
The following SQL statement calculates the access_log records in the "100":
SELECT COUNT(*) AS nums FROM access_log;
The above SQL output results are as follows:
The following SQL statement calculates the number access_log records in different site_id the Table:
SELECT COUNT(DISTINCT site_id) AS nums FROM access_log;
The above SQL output results are as follows: