How Groupby Works In Mysql

Daniel Brown
• Sunday, 01 November, 2020
• 7 min read

In other words, it reduces the number of rows in the result set. You often use the GROUP BY clause with aggregate functions such as SUM, AVG, MAX, MIN, and COUNT.

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The aggregate function that appears in the SELECT clause provides information about each group. As you can see, the GROUP BY clause returns unique occurrences of status values.

The aggregate functions allow you to perform the calculation of a set of rows and return a single value. The GROUP BY clause is often used with an aggregate function to perform calculation and return a single value for each subgroup.

For example, if you want to know the number of orders in each status, you can use the COUNT function with the GROUP BY clause as follows: To get the total amount of all orders by status, you join the orders table with the order details table and use the SUM function to calculate the total amount.

We included only orders with shipped status in the total sales. Standard SQL does not allow you to use an alias in the GROUP BY clause, however, MySQL supports this.

For example, the following query extracts the year from the order date. MySQL also allows you to sort the groups in ascending or descending orders while the standard SQL does not.

mysql max function aggregate grouping script functions w3resource
(Source: www.w3resource.com)

Notice that we used Disc in the GROUP BY clause to sort the status in descending order. You can use COUNT, SUM, AVG, etc., functions on the grouped column.

Now, suppose based on the above table we want to count number of days each employee did work. But this is not serving our purpose, we want to display total number of pages typed by each person separately.

For displaying the result set with GROUP BY Month clause we will use this syntax which is described as follows: The MySQL operator DATE_FORMAT() is used here so that it will be easy enough to group the timestamp, date, or date time table column implementing any format needed by your result to show in the query section.

Tableware denotes the particular database table involved in the GROUP BY Month clause. Colonnade defines the table column which you want to group using the month or year formats.

The column data type should have either, DATE TIME, TIMESTAMP or DATE so that while using the GROUP BY Month clause the month part can be properly extracted based on the column from the table data in database. We can even sort the result set or date column values either using ASC or Disc options.

sql condition example mysql stack
(Source: stackoverflow.com)

It helps to provide summary of type of data that we want to retrieve from the tables based on any table field or column values or it may be any aggregate functions used like AVG, SUM, MIN, MAX, etc. Normally, the MONTH() function is defined to identity every month and aggregate functions helps to show the calculative values of sum, average, minimum, maximum and so on.

Now, we will view all the records from this table DemoGroupMonth by applying the SELECT statement as follows. As you can see the DATE column values are displayed in the result set by grouping with month and in descending order.

Suppose, we want to count the number of records of the table to be determined or calculated using a specific period of time such as a Day, Month or Year parts of DATE function where the column will be having DATE TIME, DATE or TIMESTAMP field data type, then the simple query will be as follows. For this we have again inserted some rows in the table having year equal to 2023 to make the result properly runs as.

Assume that we have a table in our database as Employee which includes fields such as Person_ID, Employee_Name, Salary, Joint. Here the Joint column of the table contains DATE data type values to perform the grouping of rows by month.

Here we discuss the introduction to MySQL GROUP BY month, how does it work along with query examples. MySQL GROUP BY Count is a MySQL query that is responsible to show the grouping of rows on the basis of column values along with the aggregate function Count.

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The comma-separated lists: Col_1, Col_2,…, Col_n, denotes the column values to be fetched in the result set and one of them will be defined for aggregate function and GROUP BY clause to write the proper query. The GROUP BY clause is essential when we want a collection of result set having rows with similar values arranged into subgroups type.

This method helps to decrease the number of rows in the set of results provided by MySQL. In MySQL, the aggregate function is responsible to execute the calculation of a set table rows and outputs a value.

Thus, the COUNT() function here is used with the MySQL GROUP BY clause to complete calculation and then it gives a distinct value for every subgroup formed. Using the COUNT() function with the GROUP BY clause, then the query will produce the number of values as the count for each subgroup created based on the table column values or expressions.

Example #1: Using GROUP BY Count on a single column Step 1: Suppose, we have a Customer table in the database having the fields Customer ID, CustomerName, Credit_Limit, and City, where we have some records as follows: The SQL statement to perform this information in the result set rows with the following command.

Thus, MySQL has returned a number of customers available in the table for each grouped city name. Example #2: Using GROUP BY Count on Multiple columns Step 1: Let us take another table named Books present in our MySQL database.

mysql example clause order
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Then, we will write a query to perform the grouping of columns in the table and also implementing the count function in it. The ORDER BY clause in MySQL is responsible to arrange the column values irrespective of its data type either character or numeric, in ascending or descending order as mentioned in the query part.

Here we discuss an introduction to MySQL GROUP BY Count, how does it work with query examples. Optionally it is used in conjunction with aggregate functions to produce summary reports from the database.

“” is optional; it is used to restrict the rows affected by the GROUP BY clause. In order to help understand the effect of SQL Group By clause, let's execute a simple query that returns all the gender entries from the members table.

Executing the above script in MySQL workbench against the Myflixdb gives us the following results. Executing the above script in MySQL workbench against the myflixdb gives us the following results shown below.

The GROUP BY clause operates on both the category id and year released to identify unique rows in our above example. Suppose we want the total number of males and females in our database.

mysql invalid groupby stored functions working use enter
(Source: stackoverflow.com)

Executing the above script in MySQL workbench against the myflixdb gives us the following results. The results shown below are grouped by every unique gender value posted and the number of grouped rows is counted using the COUNT aggregate function.

Suppose we want to know all the release years for movie category id 8. Executing the above script in MySQL workbench against the Myflixdb gives us the following results shown below.

Note only movies with category id 8 have been affected by our GROUP BY clause. The GROUP BY Clause is used together with the SQL SELECT statement.

Appeared AppleGrew8,3002121 gold badges6868 silver badges116116 bronze badges Aggregate functions like SUM() are computed over the members of each group.

Analogously, not technically, to keep in mind its logic, it can be thought each grouped field having some rows is put per different table, then the aggregate function carries on the tables individually. Ben Fort conspicuously states the following saying.

mysql rollup example grouping
(Source: efficiencyofthought.com)

As is DISTINCT keyword, each field specified through GROUP BY is thought as grouped and made unique at the end of the day. The aggregate function is carried out over each group, as happened in Sub's answer.

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