![]() If you know the tricks there are ways to count rows orders of magnitude faster than you do already. This article is a close look into how PostgreSQL optimizes counting. This write-up explained various implementations of the COUNT() function using different examples.Everybody counts, but not always quickly. The COUNT(*) function returns all the records, including duplicates and NULL, COUNT(col_name) returns all records excluding the NULL values, while the COUNT(DISTINCT col_name) returns only unique records. There are multiple ways to use the COUNT() function, such as COUNT(*), COUNT(col_name), and COUNT(DISTINCT col_name). The table rows can be counted using PostgreSQL's COUNT() function. Similarly, you can use the Postgres WHERE clause or HAVING clause to count the rows based on a specific condition. This is how you can calculate the number of items present in each group. For instance, grouping the bike colors and calculating the number of items for each group.Įxample: How Does the COUNT() Function Work With the GROUP BY Clause in Postgres?īy using the GROUP BY clause, let's group the items in the bike_color column and calculate the number of items in each group using the COUNT() function: SELECT bike_color, COUNT(bike_color) ![]() Use the GROUP BY clause along with the COUNT() function to calculate the number of items for every group. How to Use the Postgres COUNT() Function With GROUP BY Clause? The output shows that there are only three distinct colors in the bike_color column. ![]() Let’s execute the SELECT statement with COUNT(DISTINCT) function to count the unique records of the bike_color column: SELECT COUNT(DISTINCT bike_color) Let’s comprehend the working of the COUNT(DISTINCT) function with the below-given example.Įxample: How Does the COUNT(DISTINCT) Function Work in PostgreSQL? The below snippet illustrates the syntax of the Postgres COUNT(DISTINCT col_name) function: SELECT COUNT(DISTINCT col_name) In PostgreSQL, executing the COUNT() function along with the DISTINCT keyword will skip the duplicated records and return the unique ones only. ![]() How to Use COUNT(DISTINCT col_name) Function in Postgres? It proves that the COUNT(col_name) function counted all the rows excluding the ‘null’. The COUNT(col_name) function returns ‘9’ instead of ‘10’. Let’s implement the COUNT(col_name) function on the bike_color column: SELECT COUNT(bike_color) The below-given example will provide you more clarity about the COUNT(col_name) function.Įxample: How Does the COUNT(col_name) Function Work in PostgreSQL? The below snippet depicts the syntax of the Postgres COUNT(col_name) function: SELECT COUNT(col_name) In PostgreSQL, the COUNT(col_name) function skips the null values and returns the rest of the records, including duplicates. How to Use COUNT(col_name) Function in PostgreSQL? It proves that the COUNT(*) function counted all the rows, including the duplicates and null. The output shows that the bike_details table has 10 rows. ![]() The following query will calculate the total number of rows in the bike_details table: SELECT COUNT(*) The bike_details table has some duplicates and null values. Here are the details of the bike_details table: We have created a bike_details table that contains some redundant/duplicated data. The below snippet illustrates the syntax of the Postgres COUNT(*) function: SELECT COUNT(*)ĬOUNT(*) function will fetch all the rows(including duplicates and NULL) from the targeted table based on the specified condition.Įxample: How Does the COUNT(*) Function Work in PostgreSQL? In PostgreSQL, the COUNT(*) function is used to get all the rows, including duplicates and NULL. How to Use COUNT(*) Function in PostgreSQL? Let’s learn the working of the COUNT() function through Practical examples. Each implementation of the COUNT() function serves a different functionality. It is an aggregate function that enables us to count the rows that meet the specified condition. ![]()
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