MySQL Count Function

MySQL Count() function is an in-built aggregate function returns the number of rows that match a specified condition.It also calculate the count of non-NULL values in a particular column.

COUNT (*) - This function is used to return the count no of rows in a result set contains all Non-Null values.
COUNT (EXPRESSION ) - This function is used to returns the result set without contaning Null rows as result of expresssion
COUNT (DISTINCT) - This function returns the count of distinct rows without contaning Null rows as result of expresssion

Demo Database:

Table Name : products

product_id	product_name	product_code	price	unit	category_id
1	The Psychology	7550	250.00	Piece	1
2	Stories for Children	3098	350.00	Piece	1
3	Harry Potter	8472	275.00	Piece	1
4	Tecno Spark	9468	8000.00	Nos	2
5	Samsung Galaxy	7188	10000.00	Nos	2
6	Panasonic Eluga	3433	7000.00	Nos	2
7	Lenovo IdeaPad	6708	45000.00	Nos	3
8	ASUS Celeron Dual Core	3583	43000.00	Nos	3

COUNT (*)

Find the total number of products in the table.

SELECT COUNT(*) FROM products;

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COUNT() with WHERE Clause

Find the number of product where price is lesser than 5000.

SELECT COUNT(product_name) FROM products where price>=5000;

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COUNT (DISTINCT)

COUNT(distinct expression) only counts non-null unique values in the specified column.

SELECT COUNT(DISTINCT unit) FROM products;

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