A detailed explanation of the use of COUNT functions in MySQL
- 2020-10-31 22:01:08
- OfStack
The COUNT function of MySQL is the simplest and most useful calculation, predicting the number of records returned by one SELECT statement.
To understand that the table of EMPLOYEE_TBL considered by the COUNT function has the following records:
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)
Now to count the number of rows in this table, based on the table above, you can make the following assumptions:
mysql>SELECT COUNT(*) FROM employee_tbl ;
+----------+
| COUNT(*) |
+----------+
| 7 |
+----------+
1 row in set (0.01 sec)
Similarly, if you want to count 1, you can count 1 as the following number recorded as Zara:
mysql>SELECT COUNT(*) FROM employee_tbl
-> WHERE name="Zara";
+----------+
| COUNT(*) |
+----------+
| 2 |
+----------+
1 row in set (0.04 sec)
Note: All SQL queries are case sensitive, so it doesn't make any difference if you give ZARA or Zara in the where condition.