To get the complete status of the account, we also need to aggregate the balance of all events. This query however, is not really working because the where clause is restricted to events with type credit_set. To avoid repeating the window for every aggregate, the query uses a WINDOW clause to define a named window that can be used multiple times in the query. To make the window functions behave like a "group by" and calculate the aggregates on the entire set, the bound is defined as BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING, meaning "for the entire partition". It works by calculating the aggregates using the window function on the entire set (all rows of the account), and then fetch the first or last row using DISTINCT ON. with window functions, such as COUNT() OVER (PARTITION BY criteria), the COUNT() value is calculated per partition. Based on this partitioning, further calculations or storage operations per partition can be implemented. The query uses both DISTINCT ON and window functions. PostgreSQL Table Partitioning means we have one largest PostgreSQL table, and this table is splitting into various tables. A partition separates a data set into subsets, which don’t overlap.
SELECT DISTINCT ON ( account ) account, FIRST_VALUE (( data -> 'credit' ):: int ) OVER w, LAST_VALUE (( data -> 'credit' ):: int ) OVER w, SUM (( data -> 'credit' ):: int ) OVER w FROM event WHERE type = 'credit_set' WINDOW w AS ( PARTITION BY account ORDER BY id ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING )
Over partition by postgresql full#
If the event table is very large, performing two full table scans, and a sort and a hash join, might become slow and consume a lot of memory. PostgreSQL is unable to combine the two subqueries into a single scan of the table. The two subqueries are then joined using a hash-join. The DISTINCT ON subquery also requires a sort by account and id.
The event table is being scanned twice, once for each subquery.
Sort Key: event_1.account, event_1.id DESC The syntax of the CUMEDIST () function is as follows: CUMEDIST () OVER ( PARTITION BY partitionexpression. The ROWNUMBER() function is a window function that assigns a sequential integer to each row in a result set. > Seq Scan on event (cost=0.00.17.50 rows=750 width=36) Introduction to the PostgreSQL ROWNUMBER() function.
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