mysql kann nicht‘Null-Daten erhalten in Abfrage

Question

hier zu zeigen, ist das, was ich erreichen müssen:

person_id last_name first_name region_id region name       
    1   barnum  phineas  1  maricopa          
    2   loman   willy  2  pima           
    2   loman   willy  3  pinal          
    2   loman   willy  4  santa cruz         
    3   kay   mary   5  cochise          
    3   kay   mary   6  gila           
    3   kay   mary   7  graham          
    4   lillian  vernon  NULL  NULL 

Hier meine Tabellen sind:

Create database sales 
use sales 

create table if not exists 
    `Sales_People` 
    (`person_id` int primary key, 
    `last_name` char(16) not null, 
    `first_name` char(16) not null); 

INSERT INTO Sales_people 
    (`person_id`, `last_name`, `first_name`) 
    values 
    ('1', 'barnum', 'phineas'), 
    ('2', 'loman', 'willy'), 
    ('3', 'kay', 'mary'), 
    ('4', 'lillian', 'vernon'); 

create table if not exists 
    `Sales_Region` 
    (`region_id` int primary key, 
    `name` char(16) not null); 

INSERT INTO Sales_Region 
    (`region_id`, `name`) 
    Values 
    ('1', 'maricopa'), 
    ('2', 'pima'), 
    ('3', 'pinal'), 
    ('4', 'santa cruz'), 
    ('5', 'cochise'), 
    ('6', 'gila'), 
    ('7', 'graham'); 

create table if not exists 
    `Sales_People_Region` 
    (`person_id` int not null, 
    `region_id` int not null, 
     constraint spr_pk primary key(person_id, region_id), 
     constraint spr_fk1 foreign key(person_id) 
     references Sales_People(person_id), 
     constraint spr_fk2 foreign key(region_id) 
     references Sales_Region(region_id)); 

INSERT INTO Sales_People_Region 
    (`person_id`, `region_id`) 
    Values 
    ('1', '1'), 
    ('2', '2'), 
    ('2','3'), 
    ('2', '4'), 
    ('3', '5'), 
    ('3', '6'), 
    ('3','7'); 

create table if not exists 
    `Sales` 
    (`year` int not null, 
    `month` int not null, 
    `region_id` int not null, 
    `amount_sold` decimal(11,2), 
     constraint s_pk primary key(year, month, region_id), 
     constraint s_fk foreign key(region_id) 
     references Sales_Region(region_id)); 

INSERT INTO Sales 
    (`year`, `month`, `region_id`, `amount_sold`) 
    Values 
    ('2016', '01', '1', '800000'), 
    ('2016', '02', '1', '850000'), 
    ('2016', '03', '1', '990000'), 
    ('2016', '01', '2', '425000'), 
    ('2016', '02', '2', '440000'), 
    ('2016', '03', '2', '450000'), 
    ('2016', '01', '3', '200000'), 
    ('2016', '02', '3', '210000'), 
    ('2016', '03', '3', '220000'), 
    ('2016', '01', '4', '50000'), 
    ('2016','02', '4', '52000'), 
    ('2016', '03', '4', '55000'), 
    ('2016', '01', '5', '40000'), 
    ('2016', '02', '5', '41000'), 
    ('2016', '03', '5', '42000'), 
    ('2016', '01', '6', '3000'), 
    ('2016', '02', '6', '31000'), 
    ('2016','03', '6', '32000'), 
    ('2016', '01', '7', '20000'), 
    ('2016', '02', '7', '21000'), 
    ('2016', '03', '7', '22000'); 

hier ist mein Code:

select sales_people.person_id, `last_name`, `first_name`, sales_region.Region_id, 
    trim(sales_region.`name`) AS 'Region Name' 
    from `sales_region` 
    inner join sales_people_region 
    on sales_people_region.region_id = sales_region.region_id 
    inner join sales_people 
    on sales_people_region.`person_id` = sales_people.`person_id` 
    group by sales_region.region_id, sales_people.person_id 
    having sales_people.person_id >= '' 
    order by sales_people.person_id, sales_region.region_id asc; 

was ich bekomme:

person_id last_name first_name Region_id "Region Name" 
1   barnum  phineas   1  maricopa 
2    loman  willy   2  pima 
2  loman  willy  3  pinal 
2  loman  willy  4  "santa cruz" 
3  kay   mary  5  cochise 
3  kay   mary  6  gila 
3  kay   mary  7  graham 

Ich bekomme es nicht, damit ich die letzte person_id sehen kann, weil ihnen keine region_ids zugewiesen sind. In der Tabelle sales_people_region region_id ist ein Primärschlüssel und daher nicht null.

Wenn ich sales_people und Gruppe nach person_id abfrage, kommt sie auf.

Answer 1

Ich denke, eine äußere Verbindung würde dies beheben. Ein innerer Join erfordert, dass auf jeder Seite des Joins mindestens eine Zeile vorhanden ist; Ein linker äußerer Join wählt alle Zeilen aus der linken Tabelle einschließlich derjenigen aus, für die in der rechten Tabelle keine übereinstimmende Zeile vorhanden ist. (A rechte äußere Verknüpfung ist das Spiegelbild dieser, und eine vollständige äußere Verknüpfung wählt unerreichte Reihen von beiden Seiten.)

Diese Abfrage:

SELECT sales_people.person_id, last_name, first_name, sales_region.Region_id, 
    TRIM(sales_region.`name`) AS 'Region Name' 
    FROM sales_people 
    LEFT OUTER JOIN sales_people_region 
    on sales_people.person_id = sales_people_region.person_id 
    LEFT OUTER JOIN sales_region 
    ON sales_people_region.region_id = sales_region.region_id 
    GROUP BY sales_region.region_id, sales_people.person_id 
    HAVING sales_people.person_id != '' 
    ORDER BY sales_people.person_id, sales_region.region_id ASC;