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How to Group By Distinct Value In Postgresql?

2 minutes read

To group by distinct value in PostgreSQL, you can use the GROUP BY clause along with the DISTINCT keyword to ensure that only unique values are included in the grouping. This can be helpful when you want to group your data based on unique values in a particular column. By using GROUP BY column_name and SELECT DISTINCT column_name, you can achieve the desired result of grouping by distinct values in PostgreSQL.


How to create custom aggregate functions for distinct values in PostgreSQL?

To create a custom aggregate function for distinct values in PostgreSQL, you can follow these steps:

  1. Define the custom aggregate function with the CREATE AGGREGATE statement. Here's an example of creating a custom aggregate function that concatenates distinct values into a string:
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CREATE AGGREGATE distinct_concat(text)
(
    SFUNC = array_append,
    STYPE = text[],
    INITCOND = '{}',
    FINALFUNC = array_to_string
);


  1. Write the state transition function (SFUNC) that adds a new distinct value to the state. In this example, we use the array_append function to add a new value to the array.
  2. Define the state type (STYPE) as an array of text values to store unique values.
  3. Specify the initial condition (INITCOND) for the array.
  4. Define the final function (FINALFUNC) to convert the array of distinct values into a concatenated string. In this example, we use the array_to_string function.
  5. Once you have created the custom aggregate function, you can use it in queries like any other aggregate function. For example: 
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SELECT distinct_concat(col_name) FROM table_name;


This query will return a concatenated string of distinct values from the specified column in the table.


By following these steps, you can create custom aggregate functions for distinct values in PostgreSQL.


What is the result of grouping by distinct value in PostgreSQL?

When you group by distinct value in PostgreSQL, the result is that only unique values are included in the grouped result set. This means that any duplicate values are removed before the grouping is applied, leading to a result set that contains only distinct values. This can be useful for aggregating data and analyzing unique values within a dataset.


How to group by distinct value in PostgreSQL?

To group by distinct value in PostgreSQL, you can use the DISTINCT keyword along with the GROUP BY clause. Here's an example query that demonstrates how to do this:

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SELECT DISTINCT column_name, COUNT(*)
FROM table_name
GROUP BY column_name;


In this query, replace column_name with the column you want to group by, and table_name with the name of the table containing that column. The DISTINCT keyword ensures that duplicate values in the column are removed before grouping.

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