Wie überschreiben Sie einen Zeilenwert, indem Sie einen Wert aus einer anderen Zeile verwenden, die aus einer anderen Tabelle stammt?

Question

Ich habe ein paar Tabellen wie folgt:

product_sets

ID | Value 
--------------- 
A | original_a 
B | original_b 
C | original_c 
D | original_d 

override_sets

ID | Name 
---------- 
X | Set 1 
Y | Set 2 

override_entries

ID | Set ID | Product ID | Override Value 
----------------------------------------- 
1 | X  | A   | new_a 
2 | X  | B   | new_b 
3 | Y  | A   | custom_a 

Ich habe bereits versucht, mit mehreren schließt sich, aber ich werde wie unten erhalten:

Product ID | Set ID | Final Value 
--------------------------------- 
A   | X  | new_a 
B   | X  | new_b 
A   | Y  | custom_a 

ich eine SQL-Ansicht final_products haben wollen, die wie unten ein Ergebnis erzeugt:

Product ID | Set ID | Final Value 
--------------------------------- 
A   | X  | new_a 
B   | X  | new_b 
C   | X  | original_c 
D   | X  | original_d 
A   | Y  | custom_a 
B   | Y  | original_b 
C   | Y  | original_c 
D   | Y  | original_d 

SQL Anweisungen:

CREATE TABLE `products` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT, 
    `value` varchar(255) COLLATE utf8_unicode_ci NOT NULL, 
    PRIMARY KEY (`id`) 
); 

CREATE TABLE `override_sets` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT, 
    `name` varchar(255) COLLATE utf8_unicode_ci NOT NULL, 
    PRIMARY KEY (`id`) 
); 

CREATE TABLE `override_entries` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT, 
    `set_id` int(10) unsigned NOT NULL, 
    `product_id` int(10) unsigned NOT NULL, 
    `value` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL, 
    PRIMARY KEY (`id`), 
    KEY `override_entries_set_id_index` (`set_id`), 
    KEY `override_entries_product_id_index` (`product_id`), 
    CONSTRAINT `override_entries_set_id_foreign` FOREIGN KEY (`set_id`) REFERENCES `override_sets` (`id`) ON DELETE CASCADE, 
    CONSTRAINT `override_entries_product_id_foreign` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`) ON DELETE CASCADE 
); 

CREATE VIEW `final_products` AS 
    SELECT 
     p.id, 
     e.set_id, 
     CASE 
      WHEN e.value IS NULL THEN p.value 
      ELSE e.value 
     END AS final_value 
    FROM products AS p 
    LEFT OUTER JOIN override_entries AS e ON p.id = e.product_id; 

Datensatz s:

INSERT INTO `products` (`id`, `value`) 
VALUES 
    (1,'original_a'), 
    (2,'original_b'), 
    (3,'original_c'), 
    (4,'original_d'); 

INSERT INTO `override_sets` (`id`, `name`) 
VALUES 
    (1,'Set 1'), 
    (2,'Set 2'); 

INSERT INTO `override_entries` (`id`, `set_id`, `product_id`, `value`) 
VALUES 
    (1,1,1,'new_a'), 
    (2,1,2,'new_b'), 
    (3,2,1,'custom_a'); 

Answer 1

Mit der angegebenen Definition und dem angegebenen Dataset verwendet die folgende Methode eine Kombination aus Kreuzverbindung (zum Verknüpfen von Tabellen ohne Beziehung) und einer Linksverbindung;

select a.id as `Product ID`, b.id as `Set Id` , 
case when c.value is null then a.value else c.value end as `Final Value` 
from products a 
cross join override_sets b 
left join override_entries c on a.id = c.product_id and b.id = c.set_id 
order by b.id, a.id; 

Answer 2

Erstellen Statements für Ihren Datensatz:

create table Product as 
select * from (select 'A' ID, 'original_a' Value 
union 
select 'B' ID, 'original_b' 
union 
select 'C' ID, 'original_c' 
union 
select 'D' ID, 'original_d') Product; 

create table Override_Set as 
select * from (select 'X' ID, 'Set 1' Name 
union select 'Y', 'Set 2') Override_Set; 

create table Override_Entry as 
select * from (select 'X' `Set ID`, 'A' `Product ID`, 'new_a' `Override_Value` 
union select 'X' `Set ID`, 'B' `Product ID`, 'new_b' `Override_Value` 
union select 'Y' `Set ID`, 'A' `Product ID`, 'custom_a' `Override_Value`) Override_Entry; 

Dies wird Ihnen das gewünschte Ergebnis:

select p.ID `Product ID`, os.ID `Set ID`, 
case when (select 1 from Override_Entry oe where concat(oe.`Set ID`,oe.`Product ID`) = concat(os.`ID`,p.`ID`)) = 1 then 
      (select `Override_Value` from Override_Entry oe where concat(oe.`Set ID`,oe.`Product ID`) = concat(os.`ID`,p.`ID`) limit 1) 
    else p.`Value` 
end desired_result 
from Product p, Override_Set os order by 2, 1; 

Sie können die Leistung beheben wollen, wenn mit einem großen Datensatz arbeiten:

+----+--------------------+-------+------+---------------+------+---------+------+------+---------------------------------------+ 
| id | select_type  | table | type | possible_keys | key | key_len | ref | rows | Extra         | 
+----+--------------------+-------+------+---------------+------+---------+------+------+---------------------------------------+ 
| 1 | PRIMARY   | os | ALL | NULL   | NULL | NULL | NULL | 2 | Using temporary; Using filesort  | 
| 1 | PRIMARY   | p  | ALL | NULL   | NULL | NULL | NULL | 4 | Using join buffer (Block Nested Loop) | 
| 3 | DEPENDENT SUBQUERY | oe | ALL | NULL   | NULL | NULL | NULL | 3 | Using where       | 
| 2 | DEPENDENT SUBQUERY | oe | ALL | NULL   | NULL | NULL | NULL | 3 | Using where       | 
+----+--------------------+-------+------+---------------+------+---------+------+------+---------------------------------------+ 

P. S. - Für eine schnellere Lösung wäre es großartig, wenn Sie create-Anweisungen für die Datensätze einfügen.