In PostgreSQL, grouping the table’s data helps us in removing redundancy. It can be done by utilizing the GROUP BY clause. However, while working with the GROUP BY clause, users often encounter a “must appear in the GROUP BY clause” error. The stated error can occur because of inappropriate use of the GROUP BY clause or aggregate functions.

This article will present a detailed guide on fixing the “must appear in the GROUP BY clause” Error in PostgreSQL.

How to Fix the “must appear in the GROUP BY clause” Error in Postgres?

In PostgreSQL, the stated error appears because of the following reason: a column is specified in the SELECT statement but it doesn’t appear in the GROUP BY clause or any aggregate function.

Here is a simple example that shows the stated error:

SELECT joining_date,
COUNT(emp_id) AS total_employees
FROM emp_info
GROUP BY emp_id;

To fix this error, the columns that are listed in the SELECT LIST must appear in the GROUP BY clause or they must appear within an aggregate function. For example, specifying the “joining_date” column in the GROUP BY clause will rectify the stated error:

SELECT joining_date,
COUNT(emp_id) AS total_employees
FROM emp_info
GROUP BY joining_date;

In the above code, we utilized the “emp_id” in an aggregate function named “COUNT()”, so it wouldn’t cause any error. However, if we used it in the SELECT statement without any aggregate function and also we didn’t utilize it in the GROUP BY clause, then it will result in an error:

The output snippet confirms that the employees have been successfully grouped based on the joining_date column.

Conclusion

A "must appear in the GROUP BY clause" error occurs in PostgreSQL when a column is specified in the SELECT statement but it is not utilized in the GROUP BY clause or any aggregate function. To fix this error, the columns that are listed in the SELECT LIST must be included in the GROUP BY clause or they must be utilized with an aggregate function. This article has explained the possible reason and the suitable solution for the “must appear in the GROUP BY clause” error.