複雜的SQL查詢幫助彙總嵌套子查詢的值

Question

我有人員，公司，員工，事件和事件種類。我正在製作一份報告/跟進表，其中人員，公司和員工是行，列是事件種類。

事件類型是簡單的值，描述：「承諾捐贈」，「收到捐款」，「打電話」，「跟進」等。事件類型的排序：

CREATE TABLE event_kinds (
    id, 
    name, 
    position); 

活動舉行實際參考事件：

CREATE TABLE events (
    id, 
    person_id, 
    company_id, 
    referrer_id, 
    event_kind_id, 
    created_at); 

referrer_id是另一種參考的人。這是發送信息/提示的人，並且是一個可選字段，儘管我有時想過濾具有特定引用者的event_kind，而我不想處理其他類型的事件。

注意我沒有員工ID參考。該參考存在，但暗含。我有應用程序代碼來驗證person_id和company_id是否真的引用員工記錄。其他的表是非常基礎的：

CREATE TABLE people (
    id, name); 

CREATE TABLE companies (
    id, name); 

CREATE TABLE employees (
    id, person_id, company_id); 

我想達到以下報告：

 
         Referrer  Phoned  Promised Donated 
    Francois       Feb 16th Feb 20th Mar 1st 
    Apple (Steve Jobs) Steve Ballmer      Mar 3rd 
    IBM     Bill Gates  Mar 7th 

第一行是一個人的記錄，第二是員工，而第三個是公司。如果我要求引薦者Bill Gates處理Phoned事件種類，我只會看到第三行，而要求Steve和Phoned則不會返回行。

現在，我做3個查詢，一個爲公司，一個爲人，最後一個爲員工。我想要訂購事件種類列，但我在應用程序代碼中執行此操作，並在那裏正確顯示它。以下是我目前所在的地方：

SELECT companies.id, 
     companies.name, 
     (SELECT events.id FROM events WHERE events.referrer_id = 1470 AND events.company_id = companies.id AND events.person_id IS NULL AND events.event_kind_id = 9 ORDER BY created_at DESC LIMIT 1) event_kind_9, 
     (SELECT events.id FROM events WHERE events.company_id = companies.id AND events.person_id IS NULL AND events.event_kind_id = 10 ORDER BY created_at DESC LIMIT 1) event_kind_10, 
     (SELECT events.created_at FROM events WHERE events.referrer_id = 1470 AND events.company_id = companies.id AND events.person_id IS NULL AND events.event_kind_id = 9 ORDER BY created_at DESC LIMIT 1) event_kind_9_order 
FROM "companies" 

SELECT people.id, 
     people.name, 
     (SELECT events.id FROM events WHERE events.referrer_id = 1470 AND events.company_id IS NULL AND events.person_id = people.id AND events.event_kind_id = 9 ORDER BY created_at DESC LIMIT 1) event_kind_9, 
     (SELECT events.id FROM events WHERE events.company_id IS NULL AND events.person_id = people.id AND events.event_kind_id = 10 ORDER BY created_at DESC LIMIT 1) event_kind_10, 
     (SELECT events.created_at FROM events WHERE events.referrer_id = 1470 AND events.company_id IS NULL AND events.person_id = people.id AND events.event_kind_id = 9 ORDER BY created_at DESC LIMIT 1) event_kind_9_order 
FROM "people" 

SELECT employees.id, 
     employees.company_id, 
     employees.person_id, 
     (SELECT events.id FROM events WHERE events.referrer_id = 1470 AND events.company_id = employees.company_id AND events.person_id = employees.person_id AND events.event_kind_id = 9 ORDER BY created_at DESC LIMIT 1) event_kind_9, 
     (SELECT events.id FROM events WHERE events.company_id = employees.company_id AND events.person_id = employees.person_id AND events.event_kind_id = 10 ORDER BY created_at DESC LIMIT 1) event_kind_10, 
     (SELECT events.created_at FROM events WHERE events.referrer_id = 1470 AND events.company_id = employees.company_id AND events.person_id = employees.person_id AND events.event_kind_id = 9 ORDER BY created_at DESC LIMIT 1) event_kind_9_order 
FROM "employees" 

我寧願懷疑我做錯了。應該有一個「更容易」的方式來做到這一點。

另一個過濾標準是過濾人員/公司名稱：WHERE LOWER（companies.name）LIKE'％apple％'。

請注意，我在這裏按event_kind_9的日期排序，而次排序按人/公司名稱排序。總結：我希望對結果集進行分頁，找到每個單元格的最新事件，按照最新事件的日期排序結果集，並按公司/人員名稱，在某些事件類型中按引用來過濾，但不是其他人。

作爲參考，我使用PostgreSQL，從Ruby，ActiveRecord/Rails。儘管解決方案是純SQL。

Answer 1

對於同一個人/公司和event_kind_id是否可以有多行（例如，比爾蓋茨在07年3月和09年3月打了電話）？如果沒有，你可以這樣做：

Select Coalesce(People.name, Companies.name) As Name 
    , Referrers.name 
    , Min(Case When EventKinds.name = 'Phoned' Then Events.created_at End) As Phoned 
    , Min(Case When EventKinds.name = 'Promised' Then Events.created_at End) As Promised 
    , Min(Case When EventKinds.name = 'Donated' Then Events.created_at End) As Donated 
From Events 
    Join EventKinds 
     On EventKinds.id = Events.event_kind_id 
    Left Join People As Referrers 
     On Referrers.id = Events.referrer_id 
    Left Join People 
     On People.id = Events.person_id 
    Left Join Companies 
     On Companies.id = Events.company_id 
-- Where Companies.Name Like 'foo%' 
Group By Coalesce(People.name, Companies.name), Referrers.name