Cette commande peut potentiellement afficher des. PostgreSQL DISTINCT removes all duplicate rows and maintains only one row. SELECT address_id, max(purchased_at) max_purchased_at Lutilisation de la commande SELECT en SQL permet de lire toutes les donnes dune ou plusieurs colonnes. The PostgreSQL DISTINCT clause keeps only one row for all groups of duplicate rows. The general solution that should work in most DBMSs: SELECT t1.* FROM purchases t1
Postgresql select distinct full#
So you'll have to add the address_id to the order by.Īlternatively, if you're looking for the full row that contains the most recent purchased product for each address_id and that result sorted by purchased_at then you're trying to solve a greatest N per group problem which can be solved by the following approaches: I used and apparently my 'unique' node is consuming a lot of computation time. The DISTINCT ON expression(s) must match the leftmost ORDER BY expression(s). Postgresql - efficient select distinct Ask Question Asked 3 days ago Modified 3 days ago Viewed 44 times 0 I have a query that is taking too much time to run and I am trying to simplify it. The DISTINCT clause keeps one row for each group of duplicates. That is because using the DISTINCT keyword means that redundant data is being pulled from the database and then discarded. Note that the "first row" of each set is unpredictable unless ORDER BY is used to ensure that the desired row appears first. The DISTINCT clause is used in the SELECT statement to remove duplicate rows from a result set. A SELECT DISTINCT query is frequently a 'code smell' it indicates that something is not quite right.
DISTINCT ON ( expression ) keeps only the first row of each set of rows where the given expressions evaluate to equal.
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