[英]How to select distinct values from query and concatenate into one column
我有一個帶有category
列的表。 除了選擇客戶外,我還想在每一行上選擇類別的可能值,即該子集中類別的所有唯一值。
我的桌子看起來像這樣:
| id | name | category |
------------------------------------
| 1 | Test Client | Retail |
| 2 | Test Client 2 | Corporate |
| 3 | Test Client 3 | Retail |
| 4 | Test Client 4 | Retail |
| 5 | Test Client 5 | Leisure |
我以為GROUP_CONCAT可以解決問題:
SELECT `client`.*, GROUP_CONCAT(DISTINCT client.category) AS possible_categories
FROM (`client`)
WHERE `name` LIKE '%query%'
GROUP BY `client`.`id`
...但是它只是給我該行的類別,而不是其他行。
我可以用代碼來完成,但這是一個O(n)操作,我希望節省處理時間。 出於說明目的,這是我可以在代碼中進行的操作:
return array_unique(array_map(function($client)
{
return $client->category;
}, $clients));
理想的情況是看這樣一個表:
| id | name | category | possible_categories |
---------------------------------------------------------------
| 1 | Test Client | Retail | Retail,Corporate,Leisure |
| 2 | Test Client 2 | Corporate | Retail,Corporate,Leisure |
| 3 | Test Client 3 | Retail | Retail,Corporate,Leisure |
| 4 | Test Client 4 | Retail | Retail,Corporate,Leisure |
| 5 | Test Client 5 | Leisure | Retail,Corporate,Leisure |
假設您是指匹配名稱的可能類別:-
SELECT `client`.*, Sub1.possible_categories
FROM (`client`)
CROSS JOIN (SELECT GROUP_CONCAT(DISTINCT client.category) AS possible_categories FROM (`client`) WHERE `name` LIKE '%query%') Sub1
WHERE `name` LIKE '%query%'
請注意,LIKE中的前導通配符可能會使它運行緩慢。
如果用“可能的類別”表示所有類別,則需要分別計算它們並將其添加到:
SELECT `client`.*, cc.possible_categories
FROM `client` cross join
(select GROUP_CONCAT(DISTINCT client.category) AS possible_categories
from `client`
where `name` LIKE '%query%'
) cc
WHERE `name` LIKE '%query%'
我認為這對您有用:
SELECT id, name, category, (SELECT GROUP_CONCAT(distinct category) FROM Client) AS possible_categories
FROM client
請參閱SQLFiddle上的演示 。
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