After looking at someone else's query I noticed they were doing a group by to obtain the unique list. "Haywood J'Bleauxmie" writes: > The first SELECT does NOT work in that the distinct() is ignored. Jump to: navigation, search. PostgreSQL DISTINCT. From PostgreSQL wiki. 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 Mnemonic: DISTINCT means different which is what '<>' tests for . I have a query which selects number of records for each house. SELECT DISTINCT on two columns not exactly what I want Hi r/PostgreSQL ! 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 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. Dec 20, 2006 at 7:26 am: I have a question about the following. 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 . 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 table has an index on (clicked at time zone 'PST'). 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. (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.. After executing a select statement the resultant table returns all rows according to the provided expression. Note: The DISTINCT clause is only used with the SELECT command. The PostgreSQL distinct keyword is used to return unrepeated results of an attribute so only one instance of repeated values is displayed. The DISTINCT variation took 4X as long, used 4X the CPU, and almost 6X the reads when compared to the GROUP BY variation. If it is required to eliminate the duplicate rows from the resultant table the DISTINCT clause in PostgreSQL can be used. I am using postgres 8.1.3 Actually, I think I answered my own question already. The PostgreSQL DISTINCT clause is used with a SELECT statement to suppress duplicate values if any in a column. 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. GROUP BY vs DISTINCT; Brian Herlihy. Hard to believe. 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 trying to get a distinct set of rows from 2 tables. Is there any dissadvantage of using "group by" to obtain a unique list? Of records for each house the resultant table returns all rows according to the provided expression according! For each house on two columns not exactly what I want Hi r/PostgreSQL not exactly what I want r/PostgreSQL. 'S query I noticed they were doing a group by to obtain a unique list '... 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