The table has an index on (clicked at time zone 'PST'). GROUP BY vs DISTINCT; Brian Herlihy. SELECT DISTINCT on two columns not exactly what I want Hi r/PostgreSQL ! 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). After executing a select statement the resultant table returns all rows according to the provided expression. Pg supports two comparison statements IS DISTINCT FROM and IS NOT DISTINCT FROM, these essentially treat NULL as if it was a known value, rather than a special case for unknown. 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). The PostgreSQL DISTINCT clause is used with a SELECT statement to suppress duplicate values if any in a column. After comparing on multiple machines with several tables, it seems using group by to obtain a distinct list is substantially faster than using select distinct. 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.. Generally, SQL or Structure Query Language is the language that allows performing various operations on the data stored in the databases of the RDBMS. The distinct keyword is very useful and is often used with a SELECT statement in PostgreSQL. From PostgreSQL wiki. The PostgreSQL distinct keyword is used to return unrepeated results of an attribute so only one instance of repeated values is displayed. Jump to: navigation, search. 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 (Remember, these queries return the exact same results.) 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.. "Haywood J'Bleauxmie" writes: > The first SELECT does NOT work in that the distinct() is ignored. I am trying to get a distinct set of rows from 2 tables. I have a query which selects number of records for each house. 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 . Note: The DISTINCT clause is only used with the SELECT command. If it is required to eliminate the duplicate rows from the resultant table the DISTINCT clause in PostgreSQL can be used. Is there any dissadvantage of using "group by" to obtain a unique list? 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 … PostgreSQL DISTINCT. Hard to believe. I am using postgres 8.1.3 Actually, I think I answered my own question already. The DISTINCT variation took 4X as long, used 4X the CPU, and almost 6X the reads when compared to the GROUP BY variation. Dec 20, 2006 at 7:26 am: I have a question about the following. After looking at someone else's query I noticed they were doing a group by to obtain the unique list. Mnemonic: DISTINCT means different which is what '<>' tests for . Statement the resultant table returns all rows according to the provided expression clause in PostgreSQL can be used an! A unique list a question about the following at 7:26 am: I have question. 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