aggregate-functions

I have a table schema which includes an int array column, and a custom aggregate function which sums the array contents. In other words, given the following: CREATE TABLE foo (stuff INT[]); INSERT INTO foo VALUES ({ 1, 2, 3 }); INSERT INTO foo VALUES ({ 4, 5, 6 }); I need a "sum" function that would return { 5, 7, 9 } . The PL/pgSQL version, which works correctly, is as follows: CREATE OR REPLACE FUNCTION array_add(array1 int[], array2 int[]) RETURNS int[] AS $$ DECLARE result int[] := ARRAY[]::integer[]; l int; BEGIN --- --- First check if either input is NULL, and return the other if it is -

I have a star schema here and I am querying the fact table and would like to join one very small dimension table. I can't really explain the following: EXPLAIN ANALYZE SELECT COUNT(impression_id), imp.os_id FROM bi.impressions imp GROUP BY imp.os_id; QUERY PLAN -------------------------------------------------------------------------------------------------------------------------------------- HashAggregate (cost=868719.08..868719.24 rows=16 width=10) (actual time=12559.462..12559.466 rows=26 loops=1) -> Seq Scan on impressions imp (cost=0.00..690306.72 rows=35682472 width=10) (actual time=0

One of the nice things relational databases support are the aggregate functions like count, sum, avg etc. But it seems that if you are using GAE, when inserting or updating a record you must calculate and store the count, sum, avg, etc. values of the whole table. But what if you have many conditional groupings? Given a Person: class Person { @Id Integer age; String city; } If I want the total number of persons and the average age Is it correct that everytime I create, update or delete a person I should also calculate both aggregates and store them as separate columns in the same table. If I

select count(*) from mytable; select count(table_id) from mytable; //table_id is the primary_key both query were running slow on a table with 10 million rows. I am wondering why since wouldn't it easy for mysql to keep a counter that gets updated on all insert,update and delete? and is there a way to improve this query? I used explain but didn't help much. As cherouvim pointed out in the comments, it depends on the storage engine. MyISAM does keep a count of the table rows, and can keep it accurate since the only locks MyISAM supports is a table lock. InnoDB however supports transactions, and

I have a single table which stores bandwidth usage on the network over a period of time. One column will contain the date time (primary key) and another column will record the bandwidth. Data is recorded every minute. We will have other columns recording other data at that moment in time. If the user requests the data on 15 minute intervals (within a 24 hour period given start and end date), is it possible with a single query to get the data I require or would I have to write a stored procedure/cursor to do this? Users may then request 5 minute intervals data etc. I will most likely be using

I am looking for clarification on this. I am writing two queries below: We have a table of employee name with columns ID , name , salary 1. Select name from employee where sum(salary) > 1000 ; 2. Select name from employee where substring_index(name,' ',1) = 'nishant' ; Query 1 doesn't work but Query 2 does work. From my development experience, I feel the possible explanation to this is: The sum() works on a set of values specified in the argument. Here 'salary' column is passed , so it must add up all the values of this column. But inside where clause, the records are checked one by one , like