What is count (*) in mysql?
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Copyright 1999-2022 by Refsnes Data. All Rights Reserved. MySQL Count() FunctionMySQL count() function is used to returns the count of an expression. It allows us to count all rows or only some rows of the table that matches a specified condition. It is a type of aggregate function whose return type is BIGINT. This function returns 0 if it does not find any matching rows. We can use the count function in three forms, which are explained below:
Let us discuss each in detail. COUNT(*) Function: This function uses the SELECT statement to returns the count of rows in a result set. The result set contains all Non-Null, Null, and duplicates rows. COUNT(expression) Function: This function returns the result set without containing Null rows as the result of an expression. COUNT(distinct expression) Function: This function returns the count of distinct rows without containing NULL values as the result of the expression. SyntaxThe following are the syntax of the COUNT() function: Parameter explanationaggregate_expression: It specifies the column or expression whose NON-NULL values will be counted. table_name: It specifies the tables from where you want to retrieve records. There must be at least one table listed in the FROM clause. WHERE conditions: It is optional. It specifies the conditions that must be fulfilled for the records to be selected. MySQL count() function exampleConsider a table named "employees" that contains the following data. Let us understand how count() functions work in MySQL. Example1 Execute the following query that uses the COUNT(expression) function to calculates the total number of employees name available in the table: Output: Example2 Execute the following statement that returns all rows from the employee table and WHERE clause specifies the rows whose value in the column emp_age is greater than 32: Output: Example3 This statement uses the COUNT(distinct expression) function that counts the Non-Null and distinct rows in the column emp_age: Output: MySQL Count() Function with GROUP BY ClauseWe can also use the count() function with the GROUP BY clause that returns the count of the element in each group. For example, the following statement returns the number of employee in each city: After the successful execution, we will get the result as below: MySQL Count() Function with HAVING and ORDER BY ClauseLet us see another clause that uses ORDER BY and Having clause with the count() function. Execute the following statement that gives the employee name who has at least two age same and sorts them based on the count result: This statement will give the output as below: Summary: in this tutorial, you will learn how to use the MySQL Introduction to the MySQL COUNT() functionThe The COUNT(*) functionThe COUNT(expression)The COUNT(DISTINCT expression)The The return type of the MySQL COUNT() function illustrationSetting up a sample tableFirst, create a table called
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insert some rows into the
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MySQL COUNT(*) exampleThe following statement uses the
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MySQL COUNT(expression) exampleIf you specify the
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MySQL COUNT() function practical examplesWe’ll use the A) Using MySQL COUNT(*) function with a GROUP BY exampleThe For example, this statement uses the
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B) Using MySQL COUNT(*) with a HAVING clause exampleTo find vendors who supply at least 9 products, you use the
C) MySQL COUNT IF exampleYou can use a control flow expression and functions e.g., See the following The following query use
Try It Out The The In this tutorial, you have learned various techniques to count the number of rows in a table using the MySQL
Was this tutorial helpful? What does count (*) mean in MySQL?MySQL COUNT() Function
The COUNT() function returns the number of records returned by a select query.
What is count (*) used for?Use the COUNT function to get the number of entries in a number field that is in a range or array of numbers. For example, you can enter the following formula to count the numbers in the range A1:A20: =COUNT(A1:A20).
Why count (*) is used in SQL?The COUNT() function is one of the most useful aggregate functions in SQL. Counting the total number of orders by a customer in the last few days, the number of unique visitors who bought a museum ticket, or the number of employees in a department, can all be done using the COUNT() function.
What is difference between count (*) and count () in SQL?The difference is simple: COUNT(*) counts the number of rows produced by the query, whereas COUNT(1) counts the number of 1 values. Note that when you include a literal such as a number or a string in a query, this literal is "appended" or attached to every row that is produced by the FROM clause.
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