Introduction to Aggregate Function in PostgreSQL
PostgreSQL aggregate functions are used to compute the set of input values in one result. It produced a single result for an entire group of tables. PostgreSQL aggregate functions used to produce a summarized set of results. They return results based on a group of rows set. Aggregate functions will treat all rows of a table as a group by default. The statement like group by clause of the select statement is used to divide all rows into smaller groups or chunks. Aggregate functions support for aggregating multiple rows in a single dataset. We can see a list of aggregate functions using \df command.
Various Aggregate Functions in PostgreSQL
Below is the list of aggregate functions in PostgreSQL is as follows.
- COUNT
- SUM
- MIN
- MAX
- AVG
Below is the detailed description of aggregate functions. Also below is the syntax of aggregate functions. We have used the customer table as an example.
Customer table:
select * from Customer;
select version();
Syntax:
- Aggregate function using the expression:
aggregate_name (expression [... , ] [order_by_clause] )
- Aggregate function using ALL –
aggregate_name (ALL expression [,...] [ order_by_clause] )
- Aggregate function using DISTINCT clause:
aggregate_name (DISTINCT expression [,...] [ order_by_clause] )
- Aggregate function using the asterisk(*):
aggregate_name (*)
Below is the parameter description are as follows.
- Aggregate name: Name of the aggregate function.
- Expression: This is the value or value of a column in aggregate function which is itself not contain any aggregate expression.
- Order by the clause: It is optional used to set to arrange results in a set of orders.
1. Count Aggregate Function
- The count aggregate function in PostgreSQL returns the count of rows from a selected number of columns.
Syntax:
COUNT (* | DISTINCT ALL | Column_name)
Below is the parameter description of syntax are as follows.
- Column name: Name of the column that we have used in the query to count the values of records.
- Asterisk (*): The Asterisk (*) indicates all the rows, it will return the count of rows of the column which have used in a query.
- DISTINCT: This clause is used to find unique value from the table, also this parameter is optional.
- ALL: This is the default clause of count aggregate function also this is optional.
Example:
1. If we want to get a total count of rows from the customer table.
testing=# select COUNT (cust_balance) from customer;
2. If we want to get a count of distinct rows for the customer balance column from the customer table.
testing=# select COUNT (distinct(cust_balance)) from customer;
3. If we want to get the count of rows for the cust_id column from the customer table.
testing=# select count(cust_id) from customer;
select count (*) from a customer;
select count (1) from a customer;
select count (cust_name) from customer;
select count (distinct(cust_name)) from customer;
2. SUM Aggregate Function
The sum aggregate function in PostgreSQL returns the sum of values from a selected number of columns. It will allow to select a total no of numeric function and return a sum of all records.
Syntax:
SUM (* | DISTINCT ALL | Column_name)
Below is the parameter description of syntax are as follows.
- Column name: Name of the column that we have used in the query to sum the values of records.
- Asterisk (*): The Asterisk (*) indicates all the rows, it will return the sum of columns that have used in a query.
- DISTINCT: This clause is used to find unique value from the table, also this parameter is optional.
- ALL: This is a default clause of SUM aggregate function, also this is optional.
Example:
1. If we want to calculate the total sum of customer balance from the customer table.
testing=# select SUM (cust_balance) from customer;
2. If we want to calculate the distinct sum of customer balance from the customer table.
testing=# select SUM(distinct(cust_balance)) from customer;
3. MIN Aggregate Function
Min function returns the result of the smallest value of all selected values of the column. It will select the lowest value from a selected column.
Syntax:
MIN (* | [DISTINCT] ALL | Column_name)
Below is the parameter description of syntax are as follows.
- Column name: Name of the column that we have used in the query.
- Asterisk (*): The Asterisk (*) indicates all the rows, it will return all rows MIN value of tables.
- DISTINCT: This clause is used to find the unique smallest value from the table.
- ALL: This is the default clause of MIN aggregate function also this is optional.
Example:
1. If we want to calculate the minimum value of customer balance from the customer table.
testing=# select MIN (cust_balance) from customer;
2. If we want to calculate the distinct minimum value of customer balance from the customer table.
testing=# select MIN(distinct(cust_balance)) from customer;
select MIN(ALL(cust_balance)) from customer;
4. MAX Aggregate Function
MAX function returns the result of the largest value of all selected values of the column. It will select the largest value from the selected column.
Syntax:
MAX (* | [DISTINCT] ALL | Column_name)
Below is the parameter description of syntax are as follows.
- Column name: Name of column.
- Asterisk (*): The Asterisk (*) indicates all the rows
- DISTINCT: This clause is used to find the unique largest value from the table.
- ALL: This is a default clause of MAX aggregate function also this is optional.
Example:
1. If we want to calculate the maximum customer balance from the customer table.
testing=# select MAX (cust_balance) from customer;
2. If we want to calculate distinct maximum customer balance from the customer table.
testing=# select MAX(distinct(cust_balance)) from customer;
select MAX(ALL(cust_balance)) from customer;
5. AVG Aggregate Function
AVG function returns the average of all selected values of the column.
Syntax:
AVG (* | [DISTINCT] ALL | Column_name)
Below is the parameter description of syntax are as follows.
- Column name: Name of the column that we have used to calculate the average.
- Asterisk (*): The Asterisk (*) indicates all the rows
- DISTINCT: This clause is used to find unique average value from the table.
- ALL: This is a default clause of the AVERAGE aggregate function also this is optional.
Example:
1. If we want to calculate the maximum customer balance from the customer table.
testing=# select AVG (cust_balance) from customer;
2. If we want to calculate distinct maximum customer balance from the customer table.
testing=# select AVG(distinct(cust_balance)) from customer;
select AVG(ALL(cust_balance)) from customer;
Conclusion
PostgreSQL aggregate function is very useful to find the result of tables. Mainly COUNT, MAX, MIN, AVG and SUM functions used in PostgreSQL. The aggregate function will support aggregate no of columns in a table. The aggregate function will produce a single result of the entire group of tables.
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This is a guide to Aggregate Functions in PostgreSQL. Here we discuss the basic concept, various aggregate functions in PostgreSQL and parameters along with respective examples. You can also go through our other related articles to learn more–
