"Haywood J'Bleauxmie" writes: > The first SELECT does NOT work in that the distinct() is ignored. I have two tables, player and card (a card represents something like a hitman's contract, with a reference to the 'killer' and the 'victim' which both reference the player table). The DISTINCT variation took 4X as long, used 4X the CPU, and almost 6X the reads when compared to the GROUP BY variation. SELECT DISTINCT on two columns not exactly what I want Hi r/PostgreSQL ! If it is required to eliminate the duplicate rows from the resultant table the DISTINCT clause in PostgreSQL can be used. EF Core currently pushes down a select expression into a subquery, since a projection would make the results different (SQL DISTINCT operates over the selected columns, whereas C# Distinct() operates on the entire entity). PostgreSQL DISTINCT. Mnemonic: DISTINCT means different which is what '<>' tests for . I am trying to get a distinct set of rows from 2 tables. After looking at someone else's query I noticed they were doing a group by to obtain the unique list. The PostgreSQL distinct keyword is used to return unrepeated results of an attribute so only one instance of repeated values is displayed. PostgreSQL wiki explain IS DISTINCT FROM: IS DISTINCT FROM and IS NOT DISTINCT FROM … treat NULL as if it was a known value, rather than … I am using postgres 8.1.3 Actually, I think I answered my own question already. Note: The DISTINCT clause is only used with the SELECT command. We can also compare the execution plans when we change the costs from CPU + I/O combined to I/O only, a feature exclusive to Plan Explorer . Is there any dissadvantage of using "group by" to obtain a unique list? GROUP BY vs DISTINCT; Brian Herlihy. The distinct keyword is very useful and is often used with a SELECT statement in PostgreSQL. After executing a select statement the resultant table returns all rows according to the provided expression. SELECT -- 3 rows a.house, -- 12 rows (for each house) a.id, -- for each ID (there are 4 repeating records) -- out of these 4 records, only 1 is unique while remaining are -- repeated records a.points FROM records a group by a.house order by a.house, a.id In this section, we are going to understand the working of the PostgreSQL DISTINCT clause, which is used to delete the matching rows or data from a table and get only the unique records.. I have a query which selects number of records for each house. Jump to: navigation, search. The PostgreSQL DISTINCT clause is used with a SELECT statement to suppress duplicate values if any in a column. The main difference between Unique and Distinct in SQL is that Unique helps to ensure that all the values in a column are different while Distinct helps to remove all the duplicate records when retrieving the records from a table.. 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