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Summary: this tutorial shows you how to use the PostgreSQL MAX function to get the maximum value of a set.

• Postgres Select Top 1
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Introduction to PostgreSQL MAX function

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PostgreSQL MAX function is an aggregate function that returns the maximum value in a set of values. The MAX function is useful in many cases. For example, to find the employees with the highest salary, or to find the most expensive products, etc.

The syntax of the MAX function is as follows:

You can use the MAX function not only in the SELECT clause but also in the WHERE and HAVING clauses. Let’s take a look at some examples of using the MAX function.

PostgreSQL MAX function examples

Let’s examine the payment table in the sample database.

The following query gets the maximum amount paid by customers in the payment table:

2	FROMpayment;

PostgreSQL MAX function in subquery

To get other information together with the maximum payment, you use a subquery as follows:

2 4 6 8 10

* payment amount=( MAX(amount) payment

First, the subquery gets the maximum payment and then the outer query selects all rows with the amount that is equal to the maximum payment returned from the subquery. The output of the query is as follows:

The following diagram illustrates the steps that PostgreSQL performs the query:

PostgreSQL MAX function with GROUP BY clause

You can combine the MAX function with GROUP BY clause to get the maximum value per group. For example, the following query gets the largest payment paid by each customer.

2 4 6

customer_id, FROM GROUP BY

PostgreSQL MAX function with HAVING clause

If you use the MAX function in a HAVING clause, you can apply a filter for the whole group. For example, the following query selects only the biggest payment paid by each customer and the biggest payments are greater than 8.99.

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customer_id, FROM GROUP BY HAVINGMAX(amount)>8.99

Finding largest values from two or more columns

Let’s take a look at an example.

First, create a new table named ranks for the demonstration. It has four columns: 1 column to store user id and other three columns to store rank from 1 to 3.

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user_idINTPRIMARYKEY, rank_2int4NOT NULL, );

Second, insert sample data into the ranks table as follows:

2 4	VALUES (2,2,8,5),

How do you get the largest rank per user as shown in the screenshot below:

To achieve this, you use GREATEST function instead of MAX function. The GREATEST function returns the greatest value from a list of values.

2 4	user_id, FROM

In this tutorial, you have learned how to use the PostgreSQL MAX function to find the maximum value of a set.

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i have table like

Postgres Select Top 1

i am inserting data from csv file where all column are same instead of id column

In case when csv file uploaded more then one time the data will be duplicate .

but id will not and id is primary key.

so I want to remove all duplicate row without using primary key .

I have to do this on single table

5 Answers

Copy distinct data to work table fk_payment1_copy. The simplest way to do that is to use into

delete all rows from fk_payment1

and copy data from fk_payment1_copy table to fk_payment1

ParadoParadoShubham BatraShubham Batra

A bit unsure about the primary key part in the question, but in any case id doesn't need to be a primary key, it just needs to be unique. As it should be since it's serial. So if it has unique values, you can do it this way:

Just need to add all columns in the select query. This way all rows that have the same values (except id) and are after this row (sorted by id) will be deleted.

Postgres Select For Update

(Also, naming a table with fk_ prefix makes it look like a foreign key.)

Sami KuhmonenSami Kuhmonen

Select Max Serial Key Sql Postgresql

if the table isn't very large you can do:

• for larger tables remove the TEMP command from the tmp_table creation
• this solution comes in handy when working with JPA (Hibernate) produced @ElementCollection which are created without primary key.

So there is a slick way right in PG wiki. https://wiki.postgresql.org/wiki/Deleting_duplicates

This query does that for all rows of tablename having the same column1, column2, and column3.

Photo Collage Max Serial Key

I was testing this on de-duping 600k rows, leading to 200k unique rows. The solution using group by and NOT IN took 3h+, this takes like 3s.

Thomas Rollet