How to use SQL GROUP BY Clause?

Question

Hubert Jason · Answer

The GROUP BY clause will gather all of the rows together that contain data in the specified column(s) and will allow aggregate functions to be performed on the one or more columns.

GROUP BY clause syntax:

SELECT column1, 
SUM(column2)
 
FROM "list-of-tables"
 
GROUP BY "column-list";

Let's say you would like to retrieve a list of the highest paid salaries in each dept:

SELECT max(salary), dept
 
FROM employee 
 
GROUP BY dept;

This statement will select the maximum salary for the people in each unique department. Basically, the salary for the person who makes the most in each department will be displayed. Their, salary and their department will be returned

Abhishek Srivasatava · Answer

Hi Allen,

Group by always used when there is any aggregate function like count.

Here is a small program to understand the logic for group by

SELECT empl_stat_cd , prsn_intn_id , count (prsn_intn_id)
FROM EE_EMPL_CAT4 
GROUP BY empl_stat_cd , prsn_intn_id

It will check that how many times prsn_intn_id is present in the column for the group of empl_stat_cd , prsn_intn_id.

After writing group we need to write the entire column name whatever we need to fetch from select statement.

If we don’t use group by then it is not possible to count error will come. In the above example if we put two column under select then count function accordingly.

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How to use SQL GROUP BY Clause?

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