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