COUNT

description

Syntax

COUNT([DISTINCT] expr)

用于返回满足要求的行的数目

example

1. MySQL > select count(*) from log_statis group by datetime;
2. +----------+
3. | count(*) |
4. +----------+
5. | 28515903 |
6. +----------+

8. MySQL > select count(datetime) from log_statis group by datetime;
9. +-------------------+
10. | count(`datetime`) |
11. +-------------------+
12. |         28521682  |
13. +-------------------+

15. MySQL > select count(distinct datetime) from log_statis group by datetime;
16. +-------------------------------+
17. | count(DISTINCT `datetime`)    |
18. +-------------------------------+
19. |                       71045   |
20. +-------------------------------+

keyword

COUNT