详细解读MySQL中COUNT函数的用法

mysql> SELECT  FROM employee_tbl;
+------+------+------------+--------------------+
| id  | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
|  1 | John | 2007-01-24 |        250 |
|  2 | Ram | 2007-05-27 |        220 |
|  3 | Jack | 2007-05-06 |        170 |
|  3 | Jack | 2007-04-06 |        100 |
|  4 | Jill | 2007-04-06 |        220 |
|  5 | Zara | 2007-06-06 |        300 |
|  5 | Zara | 2007-02-06 |        350 |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)

mysql>SELECT COUNT() FROM employee_tbl ;
+----------+
| COUNT() |
+----------+
|    7 |
+----------+
1 row in set (0.01 sec)

mysql>SELECT COUNT() FROM employee_tbl
  -> WHERE name="Zara";
+----------+
| COUNT() |
+----------+
|    2 |
+----------+
1 row in set (0.04 sec)