Counting : COUNT « Aggregate Functions « SQL / MySQL

1. SQL / MySQL
2. Aggregate Functions
3. COUNT

Counting

       
mysql>
mysql>
mysql>
mysql> CREATE TABLE sales_rep(
    ->   employee_number INT,
    ->   surname VARCHAR(40),
    ->   first_name VARCHAR(30),
    ->   commission TINYINT
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql>
mysql> INSERT INTO sales_rep values(4,'Rive','Mongane',10);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales_rep values(5,'Smith','Mike',12);
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> SELECT COUNT(surname) FROM sales_rep;
+----------------+
| COUNT(surname) |
+----------------+
|              2 |
+----------------+
1 row in set (0.00 sec)

mysql>
mysql> SELECT COUNT(*) FROM sales_rep;
+----------+
| COUNT(*) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)

mysql>
To count the number of distinct surnames, you combine COUNT() with DISTINCT, as follows:
mysql>
mysql> SELECT COUNT(DISTINCT surname) FROM sales_rep;
+-------------------------+
| COUNT(DISTINCT surname) |
+-------------------------+
|                       2 |
+-------------------------+
1 row in set (0.00 sec)

mysql>
mysql> drop table sales_rep;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>

   
    
    
    
    
    
    
  

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