Postgresql count distinct. count() Generated query would still look different .

Postgresql count distinct I'd like to group by the different 'items' and count the number of records that contain that 'item'. To run window function for distinct values I should get first value from each peer. To complete this I aggregate IDs of rows for this peer lag this aggregation by one Mark rows that are not aggregated yet (this is first row at peer) as _distinct sum ( ) FILTER ( WHERE _distinct ) over ( ) Voila. Nov 24, 2013 · I am trying to find the number of distinct values in each column of a table. It can perform tasks such as updating data on a database or retrieving data from a database. postgresql group-by distinct edited Jun 5, 2018 at 13:17 Sylvain Bugat 8,34433332 asked Jul 7, 2017 at 4:12 user1817188 5171714 1 Answer Mar 12, 2014 · Are you trying to count the people or the awards? In other words, is the result "2" because person 1 has 2 awards, or because there are 2 people that have awards? fairly new to PostgreSQL and trying out a few count queries. user_agent). Jun 1, 2018 · I have a table with duplicate entries and the objective is to get the distinct entries based on the latest time stamp. It allows developers and database analysts to quantify the number of records in a dataset fulfilling certain criteria, providing an essential measure for reporting and insight purposes. Aug 1, 2023 · PostgreSQL COUNT (DISTINCT column) example To get the distinct amounts which customers paid, you use the COUNT(DISTINCT amount) function as shown in the following example: SELECT COUNT(DISTINCT column_name) AS some_alias FROM table_name This will count only the distinct values for that column. Quick solution: Practical example To show how to count distinct values, w Sep 9, 2024 · This tutorial explains how to count distinct values over multiple columns in PostgreSQL, including an example. In order to do this, we use the COUNT function with the DISTINCT keyword. Whether you’re counting rows in an entire table or focusing on distinct Sep 24, 2009 · SELECT COUNT(*) FROM (SELECT DISTINCT DocumentId, DocumentSessionId FROM DocumentOutputItems) AS internalQuery I need to count the number of distinct items from this table but the distinct is over two columns. So the result I'd like here would be: item count toaster 3 piano 1 car 2 tv 1 Is this doable or do I really need an items table here? Thanks! Sep 23, 2024 · Using SQL COUNT(DISTINCT) is an easy way to count distinct values in SQL. What is most seamless way to do this calc using PostgreSQ Jan 26, 2024 · You will learn how to use the PostgreSQL COUNT() function to get the number of rows that satisfy a specific condition. ip_address, Hit. Jul 21, 2009 · ERROR: DISTINCT is not implemented for window functions LINE 6: COUNT (DISTINCT handle) OVER (PARTITION BY pk_pessoas) AS ha It could be very useful to find unique references within groups of clone records. Pretty straightforward - CountD Count 351 400 With a query like this: PostgreSQL 使用 PostgreSQL 进行去重计数 在本文中，我们将介绍如何使用 PostgreSQL 数据库中的 COUNT DISTINCT 函数进行去重计数。 COUNT DISTINCT 函数用于计算指定列中不重复值的数量。 Sep 21, 2013 · Looks like sqlalchemy distinct () accepts only one column or expression. If you want some more practice, here are five examples of GROUP BY. See dbfiddle. Use an appropriate query style depending on what you want to achieve. count() Generated query would still look different Jul 31, 2024 · SQL SELECT with DISTINCT on multiple columns: Multiple fields may also be added with DISTINCT clause. Why does the following query not work? Shouldn't it be possible to Feb 12, 2014 · Is it possible to count distinct values in conjunction with window functions like OVER(PARTITION BY id)? Currently my query is as follows: SELECT congestion. *, Sep 7, 2023 · However, it is important to clarify that COUNT(DISTINCT) is used to count unique values, excluding duplicate values, and COUNT(DISTINCT) OVER(PARTITION BY) is not supported by most popular databases (like PostgreSQL, SQL Server, and Snowflake, among others). My query works fine but I was wondering if I can get the final result using just one query (without using a sub-query) Mar 24, 2021 · count distinct values over columns Ask Question Asked 4 years, 7 months ago Modified 4 years, 7 months ago Jun 1, 2022 · Counting faster with Postgres Count queries are probably the most-used aggregate queries in a relational database. name) tag. However, it has its own quirks, which we’ll explain (with examples) in this article. For instance, if the Apr 11, 2018 · Postgresでdistinct onしながらcountしようとしたらハマった PostgreSQL Last updated at 2018-04-23 Posted at 2018-04-11 Jan 9, 2025 · The regular COUNT(DISTINCT ) always performs a regular sort internally, which results in bad performance if there's a lot of duplicate values. Jul 7, 2017 · however, as discussed in postgresql COUNT (DISTINCT …) very slow, this query yield poor performance. SELECT COUNT (DISTINCT) We can also use the DISTINCT keyword in combination with the COUNT statement, which in the example below will return the number of different countries there are in the customers table. Oct 12, 2016 · Everybody counts, but not always quickly. Oct 29, 2020 · Always remember: COUNT(column name) will only count rows where the given column is NOT NULL. Table of Contents Introduction Example Tune statistics for number of distinct values See more Introduction The number of distinct values in a column is stored in the n_distinct field in pg_stats. query(Hit. I want distinct on one column but order by something else that isn't the distinct column. The examples are based on the Baeldung University schema and are compatible with In this case you can use GROUP BY to get distinct column1 values, and instead of convert the date to text you can use EXTRACT function for this purpose. Includes examples of using the `WHERE` clause, `DISTINCT` keyword, and more. *), but that's not valid SQL apparently. What happens when we use it with multiple COUNT in PostgreSQL - Examples & AI Generator Mastering the COUNT function in PostgreSQL means navigating its flexible syntax—COUNT (*), COUNT (column), COUNT (DISTINCT)—and knowing which form suits your data needs. Learn how to use it with practical examples. id) AS link_created But when I try to count with a conditional, I get a syntax error, what's the proper syntax to add a case when or some other condition to only count the distinct message ids where the messages. The DISTINCT can comes only once in a given select statement. link_label is present? Oct 26, 2023 · Introduction In this tutorial, we want to count the number of unique values of a specific column. Feb 5, 2025 · The PostgreSQL COUNT function counts number of rows or non-NULL values against a specific column from a table. Jan 6, 2024 · PostgreSQL’s powerful SELECT DISTINCT command simplifies the retrieval of unique values from a database. Jan 16, 2016 · Array integer []: how to get all distinct values in a table and count them? Ask Question Asked 9 years, 10 months ago Modified 6 years, 10 months ago Mar 4, 2024 · Summary: in this tutorial, you will learn how to tune estimated number of distinct values. Frustrating beyond belief! Aug 23, 2014 · I always get errors like "more than one row returned by a subquery used as an expression" and "set-valued function called in context that cannot accept a set" when trying to count elements in arrays when using unnest. Oct 30, 2023 · PostgreSQL provides powerful SQL functionality like COUNT(DISTINCT), DISTINCT ON, window functions, and SELECT DISTINCT to tackle these needs. Dec 8, 2017 · What exactly does source_category_count count? The number of distinct category values in category table or the number of distinct category values in the category join category_tags? Because the two numbers may differ (if there are categories that do not appear in category_tags). Learn how to use the PostgreSQL DISTINCT ON clause to return unique rows based on multiple columns. See practical examples with a sample table named emp_record and its data. It‘s a versatile tool that allows you to quickly and accurately determine the number of rows that match a specific condition, making it an essential component of many data-driven decision-making processes. The syntax is invalid for PostgreSQL and SQL Server. My table only has two columns- user_id (there can be multiple uses by one user per day) and start_time which is a timestamp that indicates the time of use. I'm looking to count and count distinct all values in a table. This article explores various strategies for achieving this goal and Aug 29, 2019 · 2 {car} 3 {car, toaster} 4 {tv} 5 {toaster} Items is an array column. Nov 28, 2018 · In terms of final result I will need one row per date with the count of distinct users on that given date and the count of distinct users in the last 30 days window. Why is it so hard in Postgres? A subquery is way too slow as it will evaluate the entire thing before returning the outer order by. SQL DISTINCTで重複行を1行のみ表示する方法で紹介したように、重複行を除きたいときはDISTINCTを使用します。 集計関数のCOUNTにDISTINCTを指定すると、同じ値が複数ある場合は1カウントとして集計します。 Sep 1, 2015 · Continue to help good content that is interesting, well-researched, and useful, rise to the top! To gain full voting privileges, May 26, 2025 · The Importance of the COUNT () Function in PostgreSQL The COUNT () function is a fundamental building block in the world of data analysis and database management. Usually, when people don't want to use distinct, they use group by instead, but I can't use that with the window functions and I'm not sure it would help anyway. 63 shows aggregate functions typically used in statistical analysis. post_id = posts. Feb 13, 2019 · How to get count of rows for each user_id select distinct on (user_id) * from some_table As in such SQL: select user_id, count(*) from some_table group by user_id Learn how to use the PostgreSQL COUNT function to efficiently count rows, non-null values, and unique entries with examples and best practices for optimized query performance. In other words, this query will be valid if for any instance of the relation R, there is only one unique tuple for every value or a (thus selecting the first tuple is deterministic: there is only one tuple). Oct 8, 2025 · SELECT COUNT (DISTINCT national_id, position) FROM Faculty; COUNT (DISTINCT national_id, position) 72 Copy The query we ran was short and elegant, but the downside is that it works only with MySQL. 3. Using Concat Dec 27, 2012 · I want to count the number of distinct items in a column subject to a certain condition, for example if the table is like this: Dec 23, 2024 · Learn to retrieve unique rows with multiple columns in PostgreSQL using DISTINCT and DISTINCT ON for customized query results. Nov 13, 2025 · The third form invokes the aggregate once for each distinct value of the expression (or distinct set of values, for multiple expressions) found in the input rows. Whether you’re working with a single column or multiple columns, understanding the nuances of distinct selections can enhance your data analysis and reporting efforts. It filters out duplicate values and improves the quality of data. Another way around is to use group_by and count. For the sum, we'd need the division by count of id s inside the sum( ), but aggregates can't be nested. If n_distinct is negative, its absolute value instead represents the fraction of values that are distinct May 8, 2024 · Lets have a table with two columns [col1, col2] with some values. Apr 19, 2024 · This tutorial shows you how to use the PostgreSQL SELECT DISTINCT clause to remove duplicate rows from a result set returned by a query. Here are the two queries. This query is running pretty slowly; it takes about 7. Jul 15, 2025 · The COUNT () function in PostgreSQL is an aggregate function used to return the number of rows that match a specified condition in a query. The best way to learn about window functions is through practice. A previously posted work-around (search the GENERAL mailing list with 'count', 'DISTINCT' and 'Herouth') adapted to your query is: SELECT count (*) FROM aro t1 WHERE int ( oid ) = ( Feb 7, 2025 · SQL COUNT() with DISTINCT: SQL COUNT() function with DISTINCT clause eliminates the repetitive appearance of a same data. Jan 8, 2025 · Citus postgresql-hll introduces a new data type, called hll, which is a HyperLogLog data structure, a fixed-size, set-like structure used for distinct value counting with tunable precision. This article will explore the various syntaxes of the COUNT () function and provide practical examples to help you understand its usage in PostgreSQL. The actual query is quite co Nov 13, 2025 · PostgreSQL will effectively evaluate output expressions after sorting and limiting, so long as those expressions are not referenced in DISTINCT, ORDER BY or GROUP BY. The SQL SELECT DISTINCT Statement The SELECT DISTINCT statement is used to return only distinct (different) values. We have already created the table student with the following data: Example 1 We want to count the number Jul 31, 2025 · Using DISTINCT and COUNT together in SQL is a common technique to count the number of unique values in one or more columns. Oct 29, 2016 · I am trying to change the count DISTINCT portion of the query below, because the current query returns WINDOW definition is not supported. date, congestion. When you use COUNT(DISTINCT ), PostgreSQL examines each row and eliminates duplicate values before counting them. This should be more efficient than using concat of two columns - with group by database would be able to use indexes if they do exist: session. This process can take a toll on performance, especially when dealing with large datasets. created_at Jun 16, 1999 · SELECT count (DISTINCT address1) from aro First find all unique instances of address1 then return just their count. Jan 4, 2024 · Introduction Eliminating duplicate rows from result sets is a common task in SQL programming, and PostgreSQL offers multiple methods for selecting distinct rows. distinct (a),b is the same as distinct a, (b) or distinct a,b and it's completely unnecessary if you combine it with group by user330315 – user330315 2022-03-01 22:35:34 +00:00 CommentedMar 1, 2022 at 22:35 2 Answers Sorted by: 4 Jun 3, 2014 · Select distinct values with count in PostgreSQL Asked 11 years, 4 months ago Modified 11 years, 4 months ago Viewed 16k times Feb 8, 2018 · Continue to help good content that is interesting, well-researched, and useful, rise to the top! To gain full voting privileges, COUNT(DISTINCT messages. Postgresql will allow this query, if and only if there is a functional dependency from a to b. In this tutorial, you'll learn how to use the PostgreSQL COUNT aggregate function to count the number of values in a set. Jul 12, 2025 · The DISTINCT ON clause in PostgreSQL allows us to retrieve unique rows based on specific columns by offering more flexibility than the standard DISTINCT clause. Combined with performance optimizations like indexes and materialized views, you can efficiently count unique values in huge datasets. DISTINCT will eliminate those rows where all the selected fields are identical. The principles of combining GROUP BY and COUNT() are outlined in this article about GROUP BY and SQL aggregate functions. It simplifies data queries, removes redundancy, and makes the results cleaner and more meaningful. Table 9. The fourth form invokes the aggregate once for each input row; since no particular input value is specified, it is generally only useful for the count(*) aggregate function. keyword_id) as total_keywords, COUNT(CASE WHEN position BETWEEN 4 AND 10 THEN position ELSE NULL END ) AS pos4, date(pr. COUNT (column name) vs COUNT (DISTINCT column_name) You can probably imagine what the difference between those Sep 10, 2008 · OTOH, GROUP BY, DISTINCT or DISTINCT ON () treat NULL values as equal. This method is often used for reporting categories, users, or identifiers in a database without duplicates. The extension currently supports only data types passed by value Ugh me too, this has been plaguing me for weeks now. project_id, COUNT(DISTINCT pr. The Postgres COUNT() function counts the number of rows in a result set or the number of non-null values in a specific column. id GROUP BY posts. I would like to get number of unique values from both columns. week_nb, congestion. Oct 26, 2021 · Not exctly. More: How to delete duplicate rows without unique identifier Nov 14, 2023 · The following query works, but using distinct causes the query to take longer. This is a powerful technique for data analysis and reporting. values in col1 and col2 can be repeated. For these dialects, we’ll need to condense multiple columns into one to apply COUNT/DISTINCT. May 6, 2015 · I would like to json_agg(DISTINCT ON(tag. I would like to use the improved query (count (*) (select distinct )) as suggested in that article but I don't know how to form the query with group by. Jul 23, 2025 · GROUP BY column1: Organizes the result set into groups based on the values in column1. Counting is a fundamental operation required for many CRUD applications like … Aug 4, 2012 · SELECT COUNT(*) FROM ( SELECT COUNT(*) as count_all, posts. You get sum over DISTINCT values at target PARTITION which are Jul 21, 2009 · In response to COUNT (DISTINCT field) OVER (PARTITION BY another_field) at 2009-07-21 11:59:58 from Daniel Cristian Cruz Browse pgsql-admin by date Summary: in this tutorial, you will learn how to use the PostgreSQL COUNT() function to count the number of rows in a table. Mar 25, 2019 · I am trying to perform both count (distinct (keyword)) and count (keyword) from same tables. Learn how to use the COUNT () function and the DISTINCT clause to count only unique values in a table. Sep 2, 2023 · The issue lies in the COUNT(DISTINCT ) function, which requires more computation power and time compared to a regular COUNT() function. How then can I simulate DISTINCT ON inside an aggregate function in Postgres? Sep 22, 2013 · I realized that a database query was returning unexpected results do to my improper use of "DISTINCT ON" and "GROUP BY" I'm hoping someone can set me straight on this. Jul 10, 2024 · Mastering PostgreSQL DISTINCT? This guide dives deep with practical examples to remove duplicate rows & get you querying like a pro in no time. SQL, or Structured Query Language, is the standard language for dealing with relational databases. Query-1 SELECT t1. The count should only include users whose min (start_time) fell on that day. Sep 9, 2024 · This tutorial explains how to use COUNT DISTINCT with CASE WHEN in PostgreSQL, including an example. select Jun 22, 2015 · PostgreSQL: Combine Count and DISTINCT ON Asked 10 years, 4 months ago Modified 1 year, 8 months ago Viewed 4k times Jan 24, 2023 · In this post, we are going to see how to select distinct values from SQL queries/statements. Mar 1, 2022 · Enclosing one of the columns with parentheses won't change anything and is useless. Not on Mac? Download TablePlus for Windows. Download TablePlus for Mac. id ) as x; How would I get the number of records in this context right in PostgreSQL? Jul 21, 2025 · To count distinct values in a table, a simple SQL query can be used, combining the COUNT and DISTINCT functions along with the desired column name. In my case 'serial_no' will have duplicate entries but I select unique entries Jul 11, 2024 · can you prepare an intermediate relation using a CTE that already solves the distinct problem, and then join on it and apply a window function on one of its fields? Nov 28, 2024 · Learn common performance pitfalls and discover techniques to optimize your DISTINCT PostgreSQL queries. Simplify data counting in queries with this guide! Jan 5, 2024 · The COUNT function is a powerful and frequently used PostgreSQL aggregate function serving a fundamental role in data analysis tasks. Nov 22, 2017 · I am new to psql and am interested in counting the number of unique first time users per day. Understanding DISTINCT Clause The DISTINCT clause is a useful tool in PostgreSQL that helps retrieve unique values from a particular column or combination of columns within a result set. \ group_by(Hit. 5s, compared to SELECT COUNT(x) FROM In this article, we would like to show you how to count distinct values in PostgreSQL. This extension implements custom count_distinct aggregate function that uses an optimized sorted set to achieve the same purpose. Apr 10, 2016 · No, the result is the mean average of totals distinct on id, not the sum of total s distinct on id. Nov 2, 2023 · Introduction to SQL COUNT DISTINCT Before diving into the SQL count distinct function, let's start with the basics. In Postgres, there are ways to count orders of magnitude faster. Mar 9, 2018 · I am unclear on exactly on, SELECT DISTINCT col1, col2, FROM table_name When called on one column it gives back only distinct values of that column. 5 million rows. I have a very simple SQL query: SELECT COUNT(DISTINCT x) FROM table; My table has about 1. Even experienced analysts can lose valuable minutes recalling subtle PostgreSQL differences or coding from scratch. In this tutorial, we’ll learn how to combine DISTINCT and COUNT in an SQL query. Declaratively that is: for each column of table xyz run_query("SELECT COUNT(DISTINCT column) FROM xyz") Finding the Jul 1, 2022 · This tutorial discusses how to get the distinct count of values in a field in PostgreSQL. We’ll look at exact counts (distinct counts) as well as estimated counts, using approximation algorithms such as HyperLogLog (HLL) in Postgres. This post looks into how the PostgreSQL database optimizes counting. count (distinct (keyword)) from keyword t1, sent t2,tweets t3,u. select count (distinct co Jul 23, 2025 · The SELECT DISTINCT statement in SQL is an essential tool for retrieving unique combinations of values from multiple columns. Sep 16, 2019 · How to use COUNT DISTINCT function?Need a good GUI tool for databases? TablePlus provides a native client that allows you to access and manage Oracle, MySQL, SQL Server, PostgreSQL, and many other databases simultaneously using an intuitive and powerful graphical interface. Some common use cases include calculating the total number of records in a table, finding the number of distinct values in a column, or determining how many rows meet Nov 13, 2025 · A query like: SELECT count(*) FROM sometable; will require effort proportional to the size of the table: PostgreSQL will need to scan either the entire table or the entirety of an index that includes all rows in the table. One of the easiest ways to select distinct values is using the DISTINCT keyword. The column names col1, col2, col3 should be seen in the second table in the column col. Saddly, this is not supported by postgreSQL (yet). Oct 21, 2024 · This tutorial explains how to count the number of unique combinations across two columns in a table in PostgreSQL, including an example. I have the below select which is selecting from a table with the columns: id, project_id, keyword_id, position, Data example: i, p_id, k_id, p 1, 1, 1, 4 2, 1, 1, 5 3, 1, 1, 6 5, 1, 2, 7 6, 1, 2, 8 7, 1, 3, 5 8, 1, 3, 7 QUERY SELECT pr. It's useful for data analysis, reporting, and understanding the size and composition of your datasets. Jul 11, 2024 · The DISTINCT clause in PostgreSQL ensures your results contain only unique rows. You can still use this faster query with IS NOT DISTINCT FROM instead of = for any or all comparisons to make NULL compare equal. Additionally, various SQL implementations, such as MySQL, PostgreSQL, and Microsoft SQL Server, may have specific nuances or additional functions to achieve the same result. On Linux? Download TablePlus for Linux Need a I found solution. But the COUNT () function Jun 14, 2018 · SELECT a,b from R group by a; And this give you a similar result. As an intermediate goal I am fine with keeping many rows per day, as then I can just use MAX () Learn how to count rows in PostgreSQL with a condition using the `COUNT ()` function. Nov 22, 2024 · Learn how to use PostgreSQL COUNT() function with examples like COUNT(*), DISTINCT, and GROUP BY. id as post_id FROM posts INNER JOIN votes ON votes. Or there is another way to write this kind of query? Example (reference is a column of record_data): SELECT group_key, record_data. hkl zjett ejqz uysbb rsousr xlylieoq zoyi snip gswfm wzmn fmhhi jou kpm penz hkyxqlkb