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How Group By Clause Works In Sql

author
Earl Hamilton
• Saturday, 07 November, 2020
• 7 min read

The Subgroup BY clause is used in collaboration with the SELECT statement to arrange identical data into groups. The basic syntax of a GROUP BY clause is shown in the following code block.

sql clause placed under
(Source: www.tutorialgateway.org)

Contents

Now again, if you want to know the total amount of salary on each customer, then the GROUP BY query would be as follows The GROUP BY clause is a command in SQL that will perform this operation.

In order to understand the working of the Group By clause, let us take the help of an example. Consider a table with name as EMPLOYEE which contains the basic details of the employee such as name, age, phone number, dob, gender, address, email id, etc.

So, in order to get only the unique values from the table, we will use the following query – Gender MaleFemaleThe Group By will group all the same values in the rows together and return only a single entry or a single row for them as it did with the “Male” and “Female” rows in the table.

This resulted in just two unique values that were present in the “gender” column i, e. Now, let us take another example of a table which contains the details of the department with which each of these employees is associated to.

Employee Department Table namehoddepartment Johnhod1ServiceMayhod2FinanceAnahod1ServicePotshod2FinanceReshod3TechTanhod5SupportRanhod3ServiceWanhod3TechTunghod3FinanceChunghod5HRSo now let us execute the below query and look for the result – Hoddepartment hod1Servicehod2Financehod3Techhod5Supporthod3Servicehod3Financehod5HRThe GROUP BY clause functions on both the hod and department to look for the unique rows in the above-mentioned scenario.

sql clause groups example function aggregation does sum table using data
(Source: launchschool.com)

If the hod is the same but the department is different, then that row is treated as a unique one. Let us take a few examples using the above two mentioned tables i.e, EMPLOYEE and Employee_Department.

Namehoddepartment Mayhod2FinancePotshod2FinanceTunghod3Finance Using the GROUP BY Clause with the SELECT statement we can group rows with the same values along with the use of aggregate functions, constants, and expressions. Here we discuss How GROUP BY Clause works in SQL with the help of Examples and Employee tables.

Summary : in this tutorial, you will learn how to use Subgroup BY clause to group rows based on one or more columns. Grouping is one of the most important tasks that you have to deal with while working with the databases.

The GROUP BY clause is an optional clause of the SELECT statement that combines rows into groups based on matching values in specified columns. You often use the GROUP BY in conjunction with an aggregate function such as MIN, MAX, AVG, SUM, or COUNT to calculate a measure that provides the information for each group.

It is not mandatory to include an aggregate function in the SELECT clause. However, if you use an aggregate function, it will calculate the summary value for each group.

sql clause example complex
(Source: www.tutorialgateway.org)

For example, in the shipping department, there are 2 employees holding the shipping clerk job, 1 employee holding the stock clerk job, and 4 employees holding the stock manager job. The following statement also retrieves the phone numbers but instead of using the GROUP BY clause, it uses the DISTINCT operator.

The result set is the same except that the one returned by the DISTINCT operator is not sorted. GROUP BY clause is used with the SELECT statement.

The above query will produce the below output: As you can see in the above output, the rows with duplicate Names are grouped under same NAME and their corresponding SALARY is the sum of the SALARY of duplicate rows. This means to place all the rows with same values of both the columns column1 and column2 in one group.

And those whose only SUBJECT is same but not YEAR belongs to different groups. We can use HAVING clause to place conditions to decide which group will be the part of final result-set.

See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

sql clause count columns multiple select query onettechnologiesindia rss
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Get hold of all the important CS Theory concepts for SDE interviews with the CS Theory Course at a student-friendly price and become industry ready. Optionally it is used in conjunction with aggregate functions to produce summary reports from the database.

Now that we know what the Subgroup BY clause is, let's look at the syntax for a basic group by query. “” is optional; it is used to restrict the rows affected by the GROUP BY clause.

In order to help understand the effect of Subgroup 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. Executing the above script in MySQL workbench against the myflixdb gives us the following results.

sql clause example order
(Source: www.tutorialgateway.org)

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 SELECT statement used in the GROUP BY clause can only be used contain column names, aggregate functions, constants and expressions. In this blog, we will discuss how to work with GROUP BY, WHERE, and HAVING clauses in SQL and explain the concept with an example in a simple way.

I hope this is very useful for beginners and intermediates to help them understand the basic concept. This clause works with the select specific list of items, and we can use HAVING, and ORDER BY clauses.

Group by clause always works with an aggregate function like MAX, MIN, SUM, AVG, COUNT. MAX()- function returns the maximum value of the numeric column of specified criteria.

sql having clause oracle
(Source: www.youtube.com)

MIN()- function returns the minimum of the numeric column of specified criteria. AVG()- function returns the average value of a numeric column of specified criteria.

COUNT()- function returns the number of rows that match specified criteria. This clause works with the select specific list of items, for that we can use HAVING, and ORDER BY clauses.

Where clause works with select clause but won’t work on the group by or aggregate function condition. Having clause works with a group by clause but specifically works on aggregate function condition.

I hope you understand the concept, please post your feedback, questions, or comments about this blog and feel free to tell me the required changes in this write-up to improve the content quality.

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