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MySQL GROUP BY


The MYSQL GROUP BY Clause is used to collect data from multiple records and group the result by one or more column. It is generally used in a SELECT statement.

You can also use some aggregate functions like COUNT, SUM, MIN, MAX, AVG etc. on the grouped column.

Syntax:

  1. SELECT expression1, expression2, … expression_n,
  2. aggregate_function (expression)
  3. FROM tables
  4. [WHERE conditions]
  5. GROUP BY expression1, expression2, … expression_n;

Parameters

expression1, expression2, … expression_n: It specifies the expressions that are not encapsulated within an aggregate function and must be included in the GROUP BY clause.

aggregate_function: It specifies a function such as SUM, COUNT, MIN, MAX, or AVG etc. tables: It specifies the tables, from where you want to retrieve the 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.

(i) MySQL GROUP BY Clause with COUNT function

Consider a table named “officers” table, having the following records.

group-by-clause1

Now, let’s count repetitive number of cities in the column address.

Execute the following query:

  1. SELECT address, COUNT(*)
  2. FROM   officers
  3. GROUP BY address;

Output:

group-by-clause2

 

(ii) MySQL GROUP BY Clause with SUM function

Let’s take a table “employees” table, having the following data.

group-by-clause3

Now, the following query will GROUP BY the example using the SUM function and return the emp_name and total working hours of each employee.

Execute the following query:

  1. SELECT emp_name, SUM(working_hours) AS “Total working hours”
  2. FROM employees
  3. GROUP BY emp_name;

Output:

group-by-clause4

(iii) MySQL GROUP BY Clause with MIN function

The following example specifies the minimum working hours of the employees form the table “employees”.

Execute the following query:

  1. SELECT emp_name, MIN(working_hours) AS “Minimum working hour”
  2. FROM employees
  3. GROUP BY emp_name;

Output:

group-by-clause5

(iv) MySQL GROUP BY Clause with MAX function

The following example specifies the maximum working hours of the employees form the table “employees”.

Execute the following query:

  1. SELECT emp_name, MAX (working_hours) AS “Minimum working hour”
  2. FROM employees
  3. GROUP BY emp_name;

Output:

group-by-clause6

(v) MySQL GROUP BY Clause with AVG function

The following example specifies the average working hours of the employees form the table “employees”.

Execute the following query:

  1. SELECT emp_name, AVG(working_hours) AS “Average working hour”
  2. FROM employees
  3. GROUP BY emp_name;

Output:

group-by-clause7

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