aggregate-functions

问题 In SQL Server 2008 I have a table CUSTOMERS that has two columns as: ID, BALANCE How can I write the query that selects the ID of the customer who has maximum balance, \" in the most effective way \"? Option 1: ORDER BY BALANCE and SELECT TOP(1) --> costs too much. Option 2: Firstly Get MAX amount , then make another query that uses the amount in where clause --> costs too much and not seem reliable. 回答1: Note : An incorrect revision of this answer was edited out. Please review all answers. A

问题 Question: I want to write a custom aggregate function that concatenates string on group by. So that I can do a SELECT SUM(FIELD1) as f1, MYCONCAT(FIELD2) as f2 FROM TABLE_XY GROUP BY FIELD1, FIELD2 All I find is SQL CRL aggregate functions, but I need SQL, without CLR. Edit:1 The query should look like this: SELECT SUM(FIELD1) as f1, MYCONCAT(FIELD2) as f2 FROM TABLE_XY GROUP BY FIELD0 Edit 2: It is true that it isn\'t possible without CLR. However, the subselect answer by astander can be

问题 I need function, that returns list of strings. I have data in table like this: Id MyString ------------------------ 1 First 2 Second 3 Third 4 Fourth I need function like this (something like this works in oracle): select LISTAGG(MyString, \', \') as myList where id < 4 That returns something like this: myList ------------------------ First, Second, Third Any ideas? 回答1: You're looking for GROUP_CONCAT() Try this: select group_concat(MyString separator ', ') as myList from table where id < 4

问题 I know that if you have one aggregate function in a SELECT statement, then all the other values in the statement must be either aggregate functions, or listed in a GROUP BY clause. I don\'t understand why that\'s the case. If I do: SELECT Name, \'Jones\' AS Surname FROM People I get: NAME SURNAME Dave Jones Susan Jones Amy Jones So, the DBMS has taken a value from each row, and appended a single value to it in the result set. That\'s fine. But if that works, why can\'t I do: SELECT Name,

问题 My app has a Events table with time-stamped events. I need to report the count of events during each of the most recent N time intervals. For different reports, the interval could be \"each week\" or \"each day\" or \"each hour\" or \"each 15-minute interval\". For example, a user can display how many orders they received each week, day, or hour, or quarter-hour. 1) My preference is to dynamically do a single SQL query (I\'m using Postgres) that groups by an arbitrary time interval. Is there

问题 I\'ve been using GROUP BY for all types of aggregate queries over the years. Recently, I\'ve been reverse-engineering some code that uses PARTITION BY to perform aggregations. In reading through all the documentation I can find about PARTITION BY , it sounds a lot like GROUP BY , maybe with a little extra functionality added in? Are they two versions of the same general functionality, or are they something different entirely? 回答1: They're used in different places. group by modifies the entire

问题 I have a problem here, and I\'m hoping there is an easy solution. I\'ll try to make this as simple as possible: A ticket belongs to an attendee Example: select * from tickets JOIN attendees ON attendee.id = tickets.attendee_id An attendee has a decimal column called \"revenue\" That said, I need to run a query that will return a variety of information about the tickets, including the total revenue. The problem is that if 2 tickets belong to the same attendee, it counts their revenue twice.

问题 I would like to create a PostgreSQL function that does something like the following: CREATE FUNCTION avg_purchases( IN last_names text[] DEFAULT \'{}\' ) RETURNS TABLE(last_name text[], avg_purchase_size double precision) AS $BODY$ DECLARE qry text; BEGIN qry := \'SELECT last_name, AVG(purchase_size) FROM purchases WHERE last_name = ANY($1) GROUP BY last_name\' RETURN QUERY EXECUTE qry USING last_names; END; $BODY$ But I see two problems here: It is not clear to me that array type is the most

问题 I have the following query: SELECT Account, Unit, SUM(state_fee), Code FROM tblMta WHERE MTA.Id = \'123\' GROUP BY Account,Unit This of course throws an exception because the Code is not in the group by clause. Each state_fee has a code. How do I get this code to display in 1 record (1 code per state_fee which is multiple state_fee per unit) as a comma-separated list? I looked into different solutions on here but I couldn\'t find any that worked with a group by . 回答1: You want to use FOR XML

问题 I have the following data: name id url John 1 someurl.com Matt 2 cool.com Sam 3 stackoverflow.com How can I write an SQL statement in Postgres to select this data into a multi-dimensional array, i.e.: {{John, 1, someurl.com}, {Matt, 2, cool.com}, {Sam, 3, stackoverflow.com}} I\'ve seen this kind of array usage before in Postgres but have no idea how to select data from a table into this array format. Assuming here that all the columns are of type text . 回答1: You cannot use array_agg() to