SQL MAX() with COUNT()

MAX() with Count function

Sample table: orders

In this part, you will see the usage of SQL COUNT() along with the SQL MAX().

Example:

To get the maximum number of agents as column alias 'mycount' from the 'orders' table with the following condition -

1. 'agent_code' should be in a group,

the following SQL statement can be used :

SELECT MAX(mycount) -- Selecting the maximum value of the column 'mycount'
FROM ( -- Subquery: Creating a derived table
    SELECT agent_code, COUNT(agent_code) AS mycount -- Selecting 'agent_code' and its count, aliased as 'mycount'
    FROM orders -- From the 'orders' table
    GROUP BY agent_code -- Grouping the results by 'agent_code'
);

Explanation:

• SELECT MAX(mycount): This line selects the maximum value of the column mycount from the result set returned by the subquery.


• (SELECT agent_code, COUNT(agent_code) AS mycount FROM orders GROUP BY agent_code): This is a subquery that generates a derived table. It selects the agent_code column and counts the occurrences of each agent_code in the orders table. The COUNT(agent_code) function is used to count the occurrences of each agent_code. The results are grouped by agent_code.


• SELECT agent_code, COUNT(agent_code) AS mycount: This line within the subquery selects the agent_code column and counts the occurrences of each agent_code in the orders table. The COUNT(agent_code) function is used to count the occurrences of each agent_code, and it is aliased as mycount.


• FROM orders: This specifies the table from which the subquery is selecting data, which is the orders table.


• GROUP BY agent_code: This line groups the results of the subquery by the agent_code column. This is necessary because we're using an aggregate function (COUNT) in conjunction with a non-aggregated column (agent_code). Grouping allows us to count the occurrences of each agent_code separately.

Output:

MAX(MYCOUNT)
------------
           7

Pictorial Presentation :

SQL MAX() and COUNT() with HAVING

Sample table: orders

To get data of 'agent_code', and number of agents for each group of 'agent_code' from the orders table with the following conditions -

'agent_code' for a group will be equal to the result of an outer query [SELECT MAX(agent_code).......] with following condition -

the outer query produce the maximum number of agents mentioned as 'mycount' from an inner query [SELECT agent_code,
COUNT(agent_code) mycount FROM orders GROUP BY agent_code] with following condition -

the inner query produced the data 'agent_code' number of agents as column alias 'mycount' from the 'orders' table with the following condition -

'agent_code' should be in a group,

the following SQL statement can be used :

SELECT agent_code, COUNT(agent_code) -- Selecting 'agent_code' and its count
FROM orders -- From the 'orders' table
GROUP BY agent_code -- Grouping the results by 'agent_code'
HAVING COUNT(agent_code) = ( -- Applying a condition on the grouped counts
    SELECT MAX(mycount) -- Selecting the maximum count from a subquery
    FROM ( -- Subquery: Creating a derived table
        SELECT agent_code, COUNT(agent_code) AS mycount -- Selecting 'agent_code' and its count, aliased as 'mycount'
        FROM orders -- From the 'orders' table
        GROUP BY agent_code -- Grouping the results by 'agent_code'
    )
);

Explanation:

• SELECT agent_code, COUNT(agent_code): This line selects the agent_code column and counts the occurrences of each agent_code in the orders table.


• FROM orders: This specifies the table from which data is being selected, which is the orders table.


• GROUP BY agent_code: This line groups the results by the agent_code column. This is necessary because we're using an aggregate function (COUNT) in conjunction with a non-aggregated column (agent_code). Grouping allows us to count the occurrences of each agent_code separately.


• HAVING COUNT(agent_code) = (...): This line filters the grouped results based on a condition. It selects groups where the count of agent_code matches the result of the subquery.


• SELECT MAX(mycount): This subquery selects the maximum value of the column mycount.


• (SELECT agent_code, COUNT(agent_code) AS mycount ... ): This is a subquery that generates a derived table. It calculates the count of occurrences of each agent_code in the orders table and aliases it as mycount.


• SELECT agent_code, COUNT(agent_code) AS mycount: This line within the subquery selects the agent_code column and counts the occurrences of each agent_code in the orders table. The COUNT(agent_code) function is used to count the occurrences of each agent_code, and it is aliased as mycount.


• FROM orders: This specifies the table from which the subquery is selecting data, which is the orders table.


• GROUP BY agent_code: This line groups the results of the subquery by the agent_code column. This is necessary because we're using an aggregate function (COUNT) in conjunction with a non-aggregated column (agent_code). Grouping allows us to count the occurrences of each agent_code separately.

Output:

AGENT_CODE COUNT(AGENT_CODE)
---------- -----------------
A002                       7

Note: Outputs of the said SQL statement shown here is taken by using Oracle Database 10g Express Edition

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